In 2010, Minnesota's Hay Lake was targeted for a 46-lb annual phosphorus reduction after nutrient pollution caused impairment. 12 years later, farm practices helped secure delisting

Hay Lake in Minnesota faced a persistent phosphorus problem that contributed to summertime algal blooms and put the shallow lake on the Clean Water Act Section 303(d) list of impaired waters. A 2012 nutrient TMDL called for a 46-pound annual reduction in phosphorus loading, equal to about 34% of the lake's annual load. Farm and land-use changes, including cropland conversion to native prairie, cover crops and shoreline buffers, helped reduce phosphorus entering the lake.

By 2022, phosphorus levels were consistently meeting Minnesota's water quality standard, and Hay Lake was removed from the impaired waters list, as per a report by U.S. EPA and Minnesota Pollution Control Agency.

Why was Hay Lake impaired?

Hay Lake is a very shallow, roughly 35-acre lake near the border of Scandia, Minnesota. Its surrounding 214-acre subwatershed is largely rural and agricultural, although land use has been shifting toward rural and large-lot residential development.

Phosphorus was the central water quality concern.

For shallow lakes in the ecoregion, the total phosphorus standard is 60 µg/L. Between 1999 and 2010, samples from Hay Lake exceeded that level 74% of the time. The high phosphorus concentrations contributed to significant algal bloom growth during the summer.

In 2010, Hay Lake was added to the Clean Water Act Section 303(d) list of impaired waters because of the phosphorus exceedances.

The problem also had implications beyond the lake itself. During periods of high water, Hay Lake contributes nutrient loads downstream through its connection with Sand Lake before the water eventually reaches the St. Croix River.

The Minnesota Pollution Control Agency prepared a nutrient Total Maximum Daily Load, or TMDL, for Hay Lake in 2012. The plan identified a target reduction of 46 pounds of phosphorus per year, or roughly 34% of the annual phosphorus load.

How did landowners reduce phosphorus?

The Carnelian-Marine-St. Croix Watershed District developed a multi-lake watershed management plan to guide pollution reduction efforts and identify areas where improvements were most needed.

Among the strategies was changing how land was used. Turf lawns and cropland could be converted into native prairie, while shoreline restoration could provide additional protection against runoff entering the lake.

Between 2014 and 2022, private landowners worked with watershed partners to install several best management practices.

Those projects included converting 1.45 acres of turf lawn to prairie, restoring 300 feet of native shoreline, establishing a one-acre prairie buffer and creating a 310-by-130-foot native prairie shoreline buffer with cattle exclusion.

Another six acres of cropland were converted to native prairie across the Hay Lake watershed.

Altogether, the project records 8.45 acres of native plant community restoration and management, 300 feet of streambank and shoreline protection, and 40,300 square feet of vegetative buffer strips.

Outreach also played an important role in getting landowners involved.

The watershed district sent newsletters to every landowner in the watershed twice a year to build awareness and encourage participation in restoration efforts. Shoreland owners held meetings in 2017 and 2019, while the Washington Conservation District offered free visits to existing project sites to encourage voluntary conservation and help with planning.

What changed after restoration?

The water quality results showed a substantial improvement.

Partnerships with private landowners and Washington County produced immediate and sustained changes, with fewer than 7% of phosphorus samples exceeding the water quality standard by 2016.

When pre- and post-2011 water quality data were compared, total phosphorus had fallen by 50%.

Chlorophyll-a concentrations also dropped sharply, declining from an average of 36 µg/L to 10 µg/L over the same period.

The data showed that the work by the Carnelian-Marine-St. Croix Watershed District and local landowners was reducing phosphorus entering Hay Lake.

Most importantly, phosphorus concentrations eventually began consistently meeting Minnesota's 60 µg/L total phosphorus standard for shallow lakes.

That improvement supported Hay Lake's removal from the Clean Water Act Section 303(d) list during the 2022 listing cycle.

The project shows how changes across a relatively small watershed can contribute to measurable improvements in lake water quality. In Hay Lake's case, prairie restoration, shoreline protection and vegetative buffers were used alongside landowner participation to address phosphorus pollution.

The original goal was a 46-pound annual phosphorus reduction. The subsequent water quality data showed that the restoration efforts had produced a much larger overall improvement, with total phosphorus falling by half compared with the earlier period.

Hay Lake's restoration was therefore not based on one project alone. It involved a series of changes made by landowners and watershed partners over several years, followed by measurable improvements in phosphorus and chlorophyll-a levels.

By 2022, the lake had reached the water quality standard needed for delisting, marking the end of its impaired-waters designation for nutrient pollution.

FAQs

Why was Hay Lake impaired?
High phosphorus levels fueled summertime algal blooms.

When was Hay Lake delisted?
It was delisted during Minnesota's 2022 listing cycle.