Darcy Running can see a little more than a foot ahead through the water when he swims near his house. He's lived on Upper Prior Lake since 1986, and can't remember anything different.
"There is a lot of algae in the water, and I think that it's been about the same over the years," he said. "It doesn't bother me."
Upper Prior Lake, Lower Prior Lake and Spring Lake form a chain that's spent years on the state's impaired waters list — a biennial compilation of bodies of water that don't meet state water quality standards.
But residents aren't too worried.
Upper Prior Lake is about to get a new restaurant, which is expected to draw customers from across the south metro. While there's excitement about the spot — the area's only lakefront restaurant — it'll look out onto waters that have been noted for high algae levels that can make the lake unsuitable for swimming and boating.
Upper Prior Lake has been on the impaired waters list since 2002. Water flowing in from Spring Lake is a big part of the problem. Spring Lake been designated as impaired since 1998, largely because of runoff from agriculture and development.
"It's been many, many years of runoff into these lakes," said Chris Zadak, watershed project manager at the Minnesota Pollution Control Agency. "So we're dealing with a lot of legacy pollutant there, too, that's accumulated on the lake bottom."
The local watershed district has been taking steps for years to improve water quality in the area, and is trying to prevent runoff into Lower Prior Lake, which is already impaired for mercury in fish. In fall 2013, it started a three-part alum treatment to mitigate phosphorus levels in Spring Lake.