Trout reproducing, but high nutrients still pose threat

Interns from Dakota County assisted with netting and keeping the fish content with buckets of fresh, cool water until they could be counted and released.Last week, Minnesota Pollution Control Agency (MPCA) stream biologists sampled fish in Rice Creek near Northfield and Trout Brook near Miesville.

Saint Olaf professors and students, along with interns with Dakota County Soil and Water Conservation District (SWCD), aided the biologists with the sampling. Together, the group netted and counted over 600 brook trout and 150 brown trout in five small reaches along the streams.

Of significance, some of the trout counted were 2-inch, young-of-year trout, indicating that stream conditions are adequate for trout reproduction. MPCA stream biologist Brenda Asmus:

I was quite surprised and impressed by the number of healthy adult fish and small young-of-the-year brook and brown trout that we found in these two streams.

Some observations were not indicative of good stream health, however. The group noticed large amounts of filamentous algae, an indication of high nutrient levels in the streams. Asmus:

Small amounts of algae are normal, but high amounts of algae can cause conditions that are stressful to fish. [This is especially the case] during warm summer days when the algae decomposes and competes with trout and aquatic insects for oxygen.

In August, MPCA stream biologists will return to Rice Creek and Trout Brook to sample insects and snails and to collect water chemistry information.

The biologists will be looking for the presence or absence of pollution sensitive fish and insects. Based on what fish and aquatic insects are found, they can get a general picture of the health of the streams. If pollution sensitive species are missing from a stream, it will be rated “impaired” and follow-up work will done to determine the specific problem.

2 thoughts on “Trout reproducing, but high nutrients still pose threat”

  1. Thanks for this info, Beth. Is the situation this year different from previous years? Would all the rain this year cause more nutrients because of run-off?

  2. Jane – Good question. Since we don’t monitor these streams for these parameters each year it is hard to say if there is a difference. What we know about Trout Brook is that it has some of the highlest nitrate levels for streams in SE MN. More rain can result in dilution as well as washing more nutrients into the streams. Depends on the timing of rainfall and when nutrients are applied to the landscape.

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