Assessing water quality with insects
Land owners can tell a lot about the health of the water in a stream or pond by color, water clarity, and dissolved oxygen levels. But there’s another good indicator – bugs. Dip a cup of water and look closely at the sample. It should be teaming with tiny life. If you have pollution, they aren’t going to be there.
Diane Oleson is a water resources educator at Penn State University. She says insects have varying tolerances to water quality.
"Dragonflies, damselflies, some of the beetles and water boatmen or water striders, they are somewhat sensitive to pollution. And then if you have poor conditions most of the time, you’re only going to find insects that we consider unpleasant like mosquito larvae, aquatic worms, midge larvae," says Oleson.
She says the best time to sample depends on water temperature and where you live, but generally it’s anywhere from early June to mid-August. Too early and it’s hard to tell the larvae apart, and if you’re too late the insects have hatched off as adults.
You can send the water sample to a lab for testing, or examine it with your own eyes and a magnifying glass. It can be a family project with just a few supplies.
"You will need a net, there are special dip nets you can get. You’ll probably want some white pans because it’s much easier to see something against white," says Oleson. "Some brushes to gently remove things that clings to rocks, because these insects have places they like to live in your streams or in your pond, so you’re going to have to sample where they want to be."
There are field guides and online sources that can help you decipher what you’re looking at.
There is a free app from the Stroud Water Research Center that can help you identify stream macroinvertebrates
Watch this video on how to test for insects in your stream or pond
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