Measuring Stream Health: Inside our Monitoring Work

Monitoring Benthic Macroinvertebrates

Every summer for the past 25 years, we visit stream sites across the watershed to sample the benthic macroinvertebrate community as a part of our Integrated Watershed Monitoring Program (IWMP).

Though it’s not an easy job, it’s an important one because it’s one way we collect information about the health of the Credit River Watershed. Come with us on our visit to Belfountain Conservation Area that included an action-packed day of benthic sampling and learn about the critical role of environmental monitoring.

What We Sample

Benthic macroinvertebrates are the insects, crayfish, snails and other creatures that live on the bottom of a stream and are important indicators of water quality. This is because they have varying tolerances to pollution. Healthy streams have a wide diversity and abundance of benthic macroinvertebrates and host populations of pollution-sensitive animals such as stonefly, caddisfly and mayfly larvae.

Sampling Location

When we arrive on site, we use a map and past photos to mark out the exact area to sample. We always sample the same location so we can track changes over time.

At each site, we collect a sample from two riffles, areas of shallow, fast-moving water and one pool, an area of deeper and slower-moving water. To understand stream habitat, we assess factors such as stream flow, the substrate of the stream bottom, such as rocks or sand and the presence of aquatic plants and algae.

Time to Sample

To collect benthic macroinvertebrates, we follow a standard method that keeps our data consistent over time and with other organizations. We use a technique called the “travelling kick and sweep,” where we kick the streambed to stir up benthic macroinvertebrates and use a net to catch them. The goal is to sample a 10-metre section of the stream in about three minutes.

What We Catch

Now comes the part we love–looking at all the benthic macroinvertebrates we collected. Here are some highlights from our sample at Belfountain:

1. Giant Stonefly (Family: Pteronarcyidae): The giant stonefly is always an exciting find. They are highly sensitive to pollution, so their presence indicates excellent water quality. They can be easily identified by their large size (two to six centimetres) and the gills around their thorax and abdomen.

2. Big Water Crayfish (Cambarus robustus): This is the largest species of native crayfish in the province. They live in rocky and fast-flowing streams and rivers across southern and central Ontario. When identifying crayfish, we’re always on the lookout for invasive crayfish species like the rusty crayfish (Faxonius rusticus), which has not yet been detected in the Credit River Watershed.

3. Broad-Winged Damselfly (Family: Calopterygidae): You may recognize these critters in their pretty jewel-toned adult form. Damselflies, like dragonflies, have specialized mouthparts that extend outwards to snatch prey from the water. Long antennae are a key feature in the nymph form of broad-winged damselflies.

Processing the Samples

Once sampling is complete, we bring our collected material back to the lab, where we carefully sort, count and identify benthic macroinvertebrates under a microscope. Looking at the overall diversity and presence of these small aquatic organisms together tells us about stream health and help us assess water quality and ecosystem conditions over time.

The data we collect is entered into a central database and analyzed alongside other environmental indicators. Benthic macroinvertebrate sampling is one of many data sets that feed into our long-term Integrated Watershed Monitoring Program. Together, these data help guide watershed management decisions and conservation actions.

Learn more about what we monitor and how the information is used to protect and restore our local environment.

By: Sofia Pereira, Crew Member, Watershed Monitoring

• Environmental Monitoring
• Integrated Watershed Monitoring Program
• Nature and Wildlife