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lake monitoring

Benthic Monitoring

Benthic Macroinvertebrates are exactly what the name suggests – bottom-dwelling spineless aquatic animals that can be seen with the naked eye. These critters spend at least part of their lives in the water attached to rocks, vegetation, sticks or burrowed into the bottom sediments of freshwater streams, lakes, or ponds. Insects like stoneflies, mayflies and craneflies only spend the larval stage of their life cycle in the water. Some enjoy years in the water to emerge only for a couple of weeks on land as adults. Others spend their whole lives in the water such as amphipods, (scuds), snails and mussels.

Benthic macroinvertebrates (benthos) are excellent water quality indicators and can tell a great deal about the biological condition of a waterbody; the main reason why it is important to evaluate them. Evaluating the abundance and diversity of benthic species is a reliable indicator because they are stationary and sensitive to changes in water quality. Healthy water bodies support a great number and diversity of macroinvertebrates that are both tolerant and intolerant of pollution. However, samples that contain only pollution-tolerant species may indicate a problem with water quality. 

Benthic monitoring is the study of the ‘bugs in the mud’ and these organisms frame the base of the aquatic food chain. Benthic Monitoring is one component of the Lake System Health program of the Muskoka Water Strategy. The District of Muskoka developed this program to enhance existing Lake Health Monitoring. Lake Vernon presently has three alternating stations that are monitored annually by volunteers in partnership with the District of Muskoka. 

Each spring on Lake Vernon, samples are collected by a trained bio-technician in the littoral zone of the lake using the “travelling-kick-and-sweep” method. The littoral zone is where the invertebrates live, such as in the substrate, sediments below the substrate, top of rocks, water’s edge, and on emergent vegetation near the shoreline. Macroinvertebrates have adapted to live in these microhabitats. Mayfly larva, for example, can crawl over slippery rocks as they eat the attached algae. 

After collection, benthos are live counted and identified using the eye, and then released or sometimes they are preserved and sorted in a lab using a microscope.  The data gathered from the Lake Vernon sample sites is sent to the Ontario Benthos Biomonitoring Network (OBBN), a large-scale collaborative research initiative led by the Dorset Environmental Science Centre in order to compare and monitor lakes and streams in watersheds across Ontario.

If you would like more information on Benthic Invertebrates, their habitat, or monitoring, please see the following resources.

Muskoka Watershed Council 
Living in Cottage Country Handbook (Muskoka Watershed Council)
Muskoka Watershed Report Card 
Does Your Shoreline Have a Natural Edge?
Native Plants & Shoreline Buffers 
Integrated watershed Management  
A Shoreline Owner’s Guide to Healthy Waterfronts 3rd ed by FOCA
Love Your Lake (Natural Shoreline)  
The Shore Primer: A Cottager’s Guide to a Healthy Waterfront  (DFO & Cottage Life)
Muskoka Water Web for lake data 

Invasive Species

It has recently been brought to the LVA’s attention that there has been an explosion of the number of Trapdoor Snails, an invasive species, in certain areas of Lake Vernon. On August 1st, two LVA volunteers helped a permanent resident, who has been vigilantly trying to remove the snails in her waterfront area, hand pick the snails from the lake. Within 30 minutes in the water, three volunteers took out a 10 litre bucket of snails.

What does this mean for our lake? These snails achieve very high densities and adversely affect aquatic food webs. They compete with native snails for food and habitat and contribute to their decline. This species also clogs screens on water intake pipes, making them an economic nuisance as well as an ecological threat.  Trapdoor Snails feed on algae and plankton, leading to clearer water but also encouraging monocultures of aquatic plant growth, which can make recreating in an area of the lake difficult.  They also carry parasites that can affect waterfowl.

How did they end up in our lake? They could have arrived on a boat hull, trailer or propeller, a live well, an aquarium, or even a dock or toy from a lake with Trapdoor Snails.  Lacking natural predators, they are prolific reproducers, producing up to 400 offspring in their lifetimes.

So, what can we do? Prevent Invasive Species from spreading. It is now provincial law that you need to drain your boat (including kayaks, canoes and sailboats) and wash it with high pressure hot water or let it dry in the sun for 5 days before taking it to another body of water. Never dump aquarium fish or plants into the lake.

If you do suspect an invasive species, please report it by phoning 1-800-563-7111 or via 

If you do have a population of Trapdoor snails on your waterfront (see description below), it is recommended that you remove them, place them in a freezer for 4-6 hours and then bury them away from the water.  Confirm that the snail you have found is, in fact, a Trapdoor Snail by sending a photo of it to the EDDMaps website.

Nets and buckets will be provided. 
6.5 cm in length
Brownish to olive-green in colour
Shell has six to seven whorls
Live ones have an operculum “trap door” that allows the snail to close itself within its shell
Can survive out of water for days by closing their shells