Over the past few years the Housatonic Valley Association (HVA) has sponsored macroinvertebrate sampling of several Housatonic River tributaries, including the Far Mill River and Indian Hole Brook in Shelton. Last weekend, myself and a few other volunteers scrubbed little bugs off of the rocks in the river for hours, which were carried by the current into our nets. Later, we picked out every bug (macroinvertebrate) we could find from the samples, placing them in ice cube trays (photos), and identified them. It's very time consuming, about 3-4 hours per sampling location, and it usually takes two people.
The type of macroinvertebrates you find says a lot about the water quality. Certain types, like stoneflies, must have very high oxygen levels at all times. Other types, like blackfly and midge larvae, can live with very little oxygen and high numbers may be found in polluted waters (including my goldfish pond).
Because we volunteers are no experts, we pick one of every type of bug we find and place it in a jar of alcohol. HVA submits the jars to the DEP, who re-identifies everything in the jar and publishes a report. Here's the 2006 report.
The good news is that both streams are oxygenated enough to support a small number of sensitive species such as common stonefly larvae. The many waterfalls and riffles of both rivers is a big factor there. The bad news is that we are not usually finding many of the most sensitive species. Most of the bugs we do find -- netspinner caddisfly, fingernet caddisfly, midge and blackfly larvae -- are indicative of unnaturally high organic loads. Think lawn fertilizer and lawn clippings getting washed into the storm sewer.
For example, near Mill Street (Gristmill Trail), we collected 5 stoneflies (good), and also about 200 netspinners, 35 fingernet caddisflies, 1 fishfly, 2 snails, 3 riffle beatles and one small minnow mayfly. These are the bugs in the ice cube trays in the picture up above (click it to enlarge). Other Far Mill River samples were taken near Route 110 and off of Roaring Brook Lane. The sample near Route 110 looked better this year than the samples we usually get.
Here's a video from last year showing how we sample the river. Sometimes we get unexpected animals. The first year we caught a baby eel. This year we caught a baby salamander and a couple of fish (blacknose dace and tesselated darter).
Update 10/9/2007: A sample collected from Means Brook at Lane Street had none of the "most wanted" species, which suggests that oxygen levels are too low to support sensitive species.