Groundwater springs are the lifeblood of our trout streams.  Trout depend upon a steady supply of cold groundwater to keep streams cool enough in summer, and warm enough in winter.  Whether large springs or small seeps, every trout stream relies upon vital inputs of groundwater.

In recent decades the rising demand for permits to remove groundwater from our aquifers has outstripped the finite supply.  Once viewed as limitless, and still mistakenly viewed this way by some, many aquifers are being depleted by excessive and unsustainable pumping.  As aquifer levels drop, the volume of natural springs entering trout streams begins to decrease.  Where unsustainable pumping continues, eventually too little groundwater remains in the aquifers to supply trout streams with the minimal base flow required to support trout and other aquatic life.  For this reason, wild trout are a good indicator of the health and sustainability of our groundwater systems.  Trout are recognized by informed individuals as finny versions of “canaries in a coal mine”, which can warn us of dangerous changes occurring underground.  Minnesota Trout Unlimited continues to fight back threats to sustainable use of groundwater.

In addition to groundwater quantity, pollution of groundwater quality can damage trout, aquatic insects and other aquatic life, not to mention human health.  Elevated levels of nitrate are of particular concern.  Trout streams, because they are so closely tied to groundwater are protected by the same federal drinking water standard of 10 milligrams per liter (10 mg/l).  The Minnesota Pollution Control Agency is still working to develop a water quality standard protective of aquatic life in streams and lakes, but scientific studies suggest that a chronic value (4 day duration) of less than 5 mg/L nitrate is needed for protection of aquatic life in coldwater (trout) streams and lakes.

Sustainable Use of Groundwater

Applications for DNR groundwater appropriation permits allowing pumping of huge volumes for irrigation have soared in the past 10 years and use is exceeding sustainability thresholds in some areas.  Some of these aquifers support valuable fisheries, such as the Straight River.  Groundwater is a public resource which landowners may make “reasonable use” of.  The amount which constitutes a reasonable use amount is set by statute and amounts above this require a permit from DNR.  State law requires DNR to permit only amounts which are sustainable and which do not deplete the aquifer or negatively impacts connected aquatic systems such as trout streams.

What’s next?

During 2024 MNTU is actively working with partners to protect coldwater fisheries.

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See the MNTU blog for recent news concerning various feedlot proposals.