Fish and other aquatic life are faring well in most trout streams in the Zumbro River watershed, but there are water quality issues to work on throughout this area in southeast Minnesota, according to an MPCA study.
The agency recently posted a stressor identification report for the watershed on the following problems for fish and other aquatic life:
- Total suspended solids (TSS)
- Dissolved oxygen and eutrophication
- Flow alteration and connectivity
The most common stressor was lack of habitat, with sediment clouding the water (as measured by total suspended solids) a closely related problem. High nitrate levels, which can be toxic to fish and bugs, were also common throughout the watershed, along with changes to the way water flows and obstacles to fish migration. In a few stream sites, high water temperatures and low dissolved oxygen levels were stressing aquatic life.
The Zumbro watershed spans 1,422 square miles in Rice, Steele, Goodhue, Dodge, Olmsted, Wabasha and Mower counties. It flows northeasterly and joins the Mississippi River near Kellogg. This watershed is home to the growing city of Rochester and the famous Mayo Clinic.
The MPCA considers streams to be biologically impaired when they support less diversity and fewer numbers of fish and bugs than they should. In the Zumbro watershed, the agency identified a total of 28 streams as impaired for biology. Of those, there were 21 streams with macroinvertebrate or bug impairments, 4 with fish impairments, and 3 with both fish and bug impairments.
The conditions stressing aquatic life are largely tied to land use activities in the watershed. Some sediment issues are related to poor riparian area management, while others are more systemic. Watersheds that have a high degree of human alterations seem most at risk for not only habitat and suspended sediment, but nitrate issues as well. Overall, the stressors will need to be addressed in various ways depending on the location in the watershed.
For the Zumbro River and its tributaries, three high priority strategies to improve fish and bug conditions are:
- Focus on reducing sediment eroding from areas along streams, such as cattle pastures, and directly from streambanks. Erosion from streambanks often occurs because of increased flows from cropland drainage and more frequent storms.
- Re-establish high-quality habitat along streams, planting native vegetation such as trees and tall plans to hold soil in place and reduce erosion; shade the water and help keep the water cooler; and increase woody debris used by fish and bugs for many purposes.
- Plant cover crops, better manage nutrients from fertilizer and manure, and implement other practices to reduce nitrate levels.