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   Freshwater Mussels

Without them, “the freshwater ecosystem will change forever.”

Tony Goldberg, a wildlife disease expert at the University of Wisconsin-Madison.

When Divers for Clean Lakes and Oceans visited Hotel Lake early in 2022, they completed two dives to remove garbage from the lake. They also brought back verbal reports and underwater video of the lake’s sides and bottom. 


In one of the north-shore bays, diver Karen reported a "granite dome" 13 feet in diameter at a depth of 14 feet. The down-sloping sides of the granite dome extended into the lower silted bottom. At this point the local conditions appear to be perfect for freshwater-mussels as an extensive bed of mussels surrounded the dome. The mussels were elongated in form, about 3 inches or more in length and medium-brown in colour. Karen noted also that they were oriented vertically sitting partially submerged in the mud-silt bottom.  


For many of us who live near or around Hotel Lake, the existence of freshwater mussels comes as no surprise.  It is possible to see these mussels while snorkeling in shallow water and discarded mussel shells are often seen in the shallows around the lake.  It may come as a surprise how important these small creatures are to the health of the lake.  Thanks to diver Karen's report on a previously unknown mussel bed, and more recent video taken by us, we can bring you this segment about freshwater mussels in Hotel Lake.



Nearly 3/4 of the 297 native freshwater mussel species in North America are believed to be imperilled. In the last century, 35 species are thought to have become extinct. This leads scientists to warn that freshwater mussels may be one of the most endangered groups of animals on earth.  In most parts of the world staggering numbers of freshwater mussels are dying. For some freshwater mollusc species at risk, the degradation of their aquatic habitats is believed to be the most likely cause but the sad truth is that no one knows really why.  Current investigations include infectious diseases, climate change, dams, invasive species, loss of host-fish, severe drought and water pollution.  Fortunately our scientific community is still working towards a full understanding.  Let's take a closer look.


Freshwater mussels protect their soft inner body with two hinged shells, called valves, which leads to them being referred to as “bivalves”.  They often live in densely populated groups or beds, partially buried in the sand, gravel or silty-bottom of a body of water.  Once established as adults, they can move short distances to escape adverse environmental conditions and can also burrow down into the lake bottom. Generally, they remain in one area for most of their lives.  Depending on the species, some can live for 100 years or more. Most live in water depths between  3 -15 feet but there are cases of beds existing deeper.  Mussel shells have various shapes and colouring. Markings and ridges on the outer shell surfaces are often present and may be used to calculate age.

Mussels rely on the presence specific or non-specific host-fish to reproduce effectively. The loss or absence of a host-fish will lead to the eventual loss of that associated mussel community.


It is rare to find more than two mussel species together in a single waterbody in the Pacific northwest.


Mussels are an important source of food for amphibious muskrats and otters. Ducks and fish also consume mussels.  Raccoons and skunks will eat mussels if they are accessible in shallow water. Freshwater mussels are largely unpalatable to humans.

Mussels in Hotel Lake

Evolutionary biologists, systematists and ecologists continue to work and make progress on how to identify species and even how to define the word ‘species’. Taxonomy is the branch of science concerned with classification, especially of organisms. Unfortunately, the term “taxonomic uncertainty” keeps cropping up when one tries to research freshwater mussels. Although only 7 species of freshwater mussels exist in the Pacific northwest, it is no simple task to positively identify the mussels in Hotel Lake.

Here is an example of taxonomic uncertainty;  mussels of the same species that live in lakes may have different appearances than the same species living in rivers.  The effects of water chemistry, flow and suspended sediment can erode mussel shell features thus creating apparent differences. Even more illuminating, is the following quote:


“Differences in the genetic make-up of isolated populations might affect their appearance, but not be sufficient to affect their ability to interbreed. In other words, they might look different, but still be the same species. Conversely, they may look similar and yet be different species.” 


The above quote is from:  Freshwater Mussels of the Pacific Northwest, Second Edition. Ethan Jay Nedeau, Allan K. Smith, Jen Stone, and Sarina Jepsen.  Published in June 2009 by The Xerces Society in Portland, Oregon.

To explore further and to begin to understand the mussels in our lake, the above document can be accessed by clicking on it.

On page 26 - 28 of the aforementioned document, the Anadonta Clade 2 (a group of organisms believed to have evolved from a common ancestor, according to the principles of cladistics), can be found to closely match our Hotel Lake mussels.  They are:

Oregon Floater Anodonta oregonensis Lea, 1838 

Western Floater Anodonta kennerlyi Lea, 1860


You can read a detailed description at the provided link followed by several photographs.  A sample mussel shell from Hotel Lake was not hard to find and it is photographed above for comparison.

Both the Oregon and Western Floaters appear similar to our sample shell. Both are known to inhabit ranges that overlap in southern British Columbia coastal areas and thus, they could indeed be what we see in Hotel Lake. The term “Floater” applies to all Anodonta species and refers to the mussel's thin and fragile shells (also referred to as valves). The light weight of these shells means that these mussels are very close to neutral buoyancy and, as such, they can “float” or maintain position precisely in the top of the soupy-thick bottom substrates of silt and mud that occur, particularly on lake bottoms.  Such precise positioning is important so that the mussel can ingest water from its top siphon and excrete from its lower.  Another characteristic of this buoyant organism is that when it dies, a build up of gasses inside the closed shell cavity can cause the deceased mussel to float to the surface.

Life Cycle of Freshwater Mussels  

Life Cycle

Our Hotel Lake mussels are long-term brooders that breed in the summer and spawn in the fall or spring.  Breeding starts when males release sperm into the water. Females “inhale” the sperm which fertilizes the eggs. Embryos develop into microscopic larvae called glochidia. At some point the female releases enormous quantities of glochidia into the water.  The glochidia must then attach themselves individually to the scales or gills of a host fish that may be swimming nearby.

No data is available on Hotel Lake but past studies on other lakes in the region found Anodonta glochidia present on Prickly Sculpin, Stickleback, Dolly Varden and Cutthroat trout.

The glochidia, after it attaches to the fish, forms a cyst around itself and, after hitch-hiking for a few weeks, detaches itself and sinks to the bottom of the lake where it burrows into the silt and mud to begin development towards maturity.  The presence of a host-fish nearby to freshwater mussel beds appears to be absolutely essential as a temporary host for the glochidia. The host fish also moves about resulting in distribution to new locations.  If the host-fish ceased to be present then the viability of the mussel bed might be destroyed.

The Anodonta glochidia, after it releases from the host fish, drops to the bottom and burrows down to start growing and will reach sexual maturity after about 5 years. Living only 10 to 15 years, our local Anodonta mussels have one of the shortest lifespans of all freshwater mussels.

For several years the Freshwater Fisheries Society of BC have been stocking Hotel Lake with Cutthroat Trout which are known to be host-fish for mussels in BC.  Stocking the lake is an excellent service that serves us all well.

And Now For The Best Part!

Clean Water

Aside from reproduction, freshwater mussels might seem a rather dull lot who spend their lives in large beds located in unseen areas of the the bottom of Hotel Lake. They are always doing the same thing every day, continuously ingesting water into their top siphon, filtering, digesting and excreting useful nutrient for underwater insects. An exhalent aperture is used to expel filtered water, fecal material, and undigestible particles back into the habitat. They continuously clean pollutants, nutrient pollution, algae, zooplankton and bacteria from the water.  All of this benefits aquatic diversity and the quality of the lake's water for wildlife and humans. During their lives these mussels absorb and retain nutrients, minerals and toxins.


These mussels number in the thousands and, cumulatively, they can represent the largest animal biomass in the waterbody where they live. Their ability to clean our lake water is apparent to anyone snorkeling over a mussel bed because the visibility in the water improves as you approach the bed. This phenomena is repeatedly demonstrated online so we have added the following short video so you can see for yourself. Considering that nearly 3/4 of the 297 native freshwater mussel species in North America are believed to be imperilled it is no wonder that some jurisdictions are already beginning to re-instate mussels into waterways where mussels had been killed-off.  The hope is that those dead waterways might be brought back to health by these hardworking bivalves. Where some jurisdictions fail to act, environmental groups have initiated lawsuits seeking action to reinstate and protect these species. 

The most prevalent threats to freshwater mussels are pollution and invasive species.

26 European countries have reported declines up to 90 percent in various mussel populations, particularly the freshwater pearl mussel.

It is largely because these mussels thrive in large populations or beds and remain sedentary, that they are so vulnerable.  They are highly sensitive to changes in their water habitat.  Any change to water quality, temperature, depth or oxygen level or to the level of chemical pollution can become a very real threat to their survival.  Mussels retain contaminants in their shells and bodies.  These may include mercury, dioxin, lead and other complex biphenyls and hydrocarbons.  Polluting contaminants can not only affect mussels directly, they may also affect the local host fish population, in which case, both mussels and fish may face elimination.  It’s worth noting at this point, that when a mussel community suddenly dies-off the decomposition of their bodies creates a brief pulse of nutrient after which the waterbody becomes darker and cloudier because the mussels are no longer filtering the water.

Invasive species are already on the horizon!

Most of us have heard about the ongoing invasion of North America by the tiny non-native zebra and quagga mussels. These tiny invaders are from the Baltic Sea region and appeared in our Great Lakes in the 1980s. Moving westward they are in 24 US states and in Quebec, Ontario and Manitoba.  Now they pose a serious threat to British Columbia’s freshwater lakes and fisheries.

The BC government responded with a program of inspections in an attempt to stop the invasion.  Since 2015, the provincial Invasive Mussel Defence Program conducted more than 220,000 inspections and reportedly stopped 137 infested watercraft from entering BC waterways. Today, calls for continued funding for this program are being heard.  At the time of the publishing of this web page in April of 2022 the government of BC states: "To date, there has been no reported introduction of live quagga or zebra mussels into B.C. lakes or waterways." Considering the invasive track record so far, it seems unlikely these invasive mussels will be stopped.

If they cannot be stopped, the consequences of their presence in waterways is well documented as stated by the BC provincial government: 

"Zebra and quagga mussels can substantially alter aquatic food webs which could result in the collapse of valuable native fish populations in B.C. such as sockeye salmon. Zebra and quagga mussel infestations can displace native aquatic plants and wildlife, degrade the environment and affect drinking water quality.

Zebra mussels have been identified as a threat to B.C.’s endangered Rocky Mountain Ridged Mussel (Gonidea angulata).

These invasives can clog pipes, water intake systems (hydropower facilities, agriculture irrigation systems), and municipal water supply. This can increase maintenance costs for operating hydroelectric, industrial and agricultural facilities. These mussels can decrease the quality of the recreational experience and impact tourism as mussel shells can injure swimmers along shorelines and next to docks, foul boat propellers and potentially harm drinking water.


The economic impact of these invasive mussels to hydropower, agricultural irrigation, municipal water supplies and recreational boating has been estimated to be $43 million per year. This estimate does not include additional impacts on commercial and recreational fisheries." end quote by BC govt.

"One of the most well documented impacts is on our native mussels.  Zebra mussels are anchoring themselves by the thousands to native mussels making it impossible for the native mussel to function. As many as 10,000 zebra mussels have attached to a single native mussel. Our natives have all but disappeared in Lake St. Clair and the western basin of Lake Erie". (Source: U.S. Geological Survey, June 2017).

Zebra and Quagga mussels readily attach boat hulls, propellers, and fishing gear and are easily transported from one waterbody to another. They can attach to pipes, docks, ladders and other structures.  They clog water systems (pipes) and can cause serious and expensive damage to hydropower and agricultural irrigation installations. They are tiny, hard to detect and hard to remove once established. There are also concerns these invasive mussels could degrade the quality of drinking water and disrupt the freshwater ecosystem by displacing native mussels and fish.

An incredible side-bar to this story features moss-balls sold in pet stores for aquarium use. These were found to be contaminated with these invasive mussels. Subsequent news reports of these invasive mussels being found in the Vancouver Aquarium underscores the difficulty of blocking them from B.C.

What can we do?


On Hotel Lake, gasoline powered motorized boats are not permitted and there is no organized boat launch for trailered-boats. Nonetheless, non-motorized watercraft like canoes, kayaks, car-toppers, paddle boards and inflatable boats are all possible hosts for invasive mussels and therefore subject to inspection under the Invasive Mussel Defence Program. It is not known if our government intends to expand the program of inspections to include watercraft arriving on the Sunshine Coast. In the meantime, we can try and stay informed and be vigilant: 


Here is a simple procedure authored by Jessica Greinke at the Freshwater Fisheries Society of B.C.

Always follow the "Clean Drain Dry" procedure for your boat, trailer and fishing gear before entering another waterbody:

  • Clean off plant parts, animals, and mud from boat and equipment (e.g. boots, waders, and fishing gear). Use a power-washing station if available.

  •  Drain onto land all items that can hold water (e.g. buckets, wells, bilges and ballast).

  •  Dry all items completely before using them in another body of water

Let's hope we can keep our freshwater mussel beds safe and healthy!

Library of references:


Freshwater Molluscs. Many freshwater mollusc species are at risk due to loss and degradation of aquatic habitats.  A brochure published in 2000 by Forest Renewal British Columbia.


The Hidden Strengths of Freshwater Mussels. An article from Knowable Magazine: The humble bivalves can clean polluted water and bump up diversity — but in dammed rivers and fouled watersheds, many species face extinction. With help, maybe they can save themselves. By Sharon Levy.


Freshwater Mussels of the Pacific Northwest, Second Edition. Ethan Jay Nedeau, Allan K. Smith, Jen Stone, and Sarina Jepsen.  Published in June 2009 by The Xerces Society in Portland, Oregon.

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