The lower St. Croix River flows from Stillwater, Minn., down to Prescott, Wisc. where it pours into the Mississippi river.
Fishing guide Bob Nasby, who has spent most of the past 40 years on the St. Croix.
"What a magnificent piece of water this is," he said. "I've fished a lot of rivers in my lifetime. But it never ceases to amaze me what it looks like when you're coming up through that valley."
The entire St. Croix River, more than 150 miles in length, is part of the National Wild and Scenic River System. Its headwaters are in Solon Springs, in northwestern Wisconsin. More than 8,000 square miles feed this river.
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Nasby's tour of it started in his truck in Woodbury, miles from the actual river. The phosphorous run-off from developments like this feed weeds and algae blooms in the St. Croix, he said. He pointed to a recent crop of subdivisions.
"The rows and rows and rows and miles of housing developments. One right after the other, that has to take a toll on that waterway. It has to," he said.
The Minnesota Pollution Control Agency recently declared the lower St. Croix River impaired by phosphorous from run-off. In Afton, the river is half a mile wide and 90 feet deep in some parts.
That's where we pulled in for a closer look. The river is still mostly frozen, so instead of touring it from a boat, we drove along a bluff-side road crowded with big homes. Many have clear-cut a view to the river.
"It's a national scenic riverway, so they are not supposed to cut trees down," Nasby said. He said there is a reason for that. "The more money you got, the more trees you [can] cut down."
Poorly-planned development is hurting both the river's beauty and its water quality, according to American Rivers. The group wants more oversight from the Minnesota and Wisconsin DNRs.
As we drove along, a bright blue rectangle appears as to jut out into the river. It stands out in the brown grass and the rocks along the river.
"That's a tennis court," Nasby said.
A fenced-in tennis court with flood lights overhead is perched on the edge of the water. From his boat on the river in warm weather, Nasby can see people playing tennis.
Molly Shodeen, a river hydrologist with the Minnesota DNR overseeing the St. Croix, describes the tennis court as evidence of the pressure on the river.
"It's a perfect example of how over time the local units of government don't step up to the plate," she said in a telephone interview.
She said the tennis court pre-dates the river's designation as a federally protected river. Until recently, vines hid the court. Then the town government gave the new owner permission to tear down the fence and resurface the court, with the condition that new vines would have to grow or be replanted on the fence within two years.
The owner made that an impossibility, Shodeen said.
"What he did was carry asphalt out three, four, five feet from the fence so there was no ability for any vines to grow."
When a local government approves a zoning variance the DNR can veto it, but property owners can then sue the DNR. And in this case, the DNR would have to sue the owner of the tennis court. It is already embattled in two State Supreme Court cases with property owners who want to build bigger structures on the edge of the bluffs overlooking the river.
The DNR opposes those structures for more than cosmetic reasons, Shodeen said.
"Bluffs on the St. Croix are all sugar sand, and they are very fragile," she said. "And when you get the river beating up the bottom of a bluff, oftentimes you can get a slide from the top."
Veto power in Minnesota isn't enough to keep the river safe, and there's not money or interest to do much more, according to Shodeen.
On the Wisconsin side of the river, the DNR has written stricter rules for development on the river, but local governments are the ones enforcing them.
Neither state is doing enough to protect the waterway, American Rivers president Rebecca Wodder said.
"These are the agencies that said years ago, when this river was protected, that they would be the watchdogs," she said. "And that they would undertake the responsibility to make sure that nothing would happen that would diminish the value for which this river was protected and they need to do that job."
Wodder says if they don't, the river will die a death of a million tiny cuts.