To the delight of trout fishermen and the chagrin of developers, Minnesota officials announced Wednesday that 20.5 more miles of the Vermillion River and tributaries are now clean enough to be designated a trout stream.

"It is a victory not only for clean water and trout, but for the people who appreciate it," said Department of Natural Resources spokesman Harland Hiemstra.

But developers think the designation is, well, fishy. The stretch of river cuts a wide swath through booming Dakota County, from Farmington into Vermillion Township. The new designation will make houses more difficult to build and more expensive, they say.

"There probably were trout in there in the 1800s, but the thing that irritates me is that they say it's such a great trout stream. But those trout were raised in a hatchery and put in that stream," said Don Patton, senior vice president of D. R. Horton, builder of homes in the Twin Cities. "It is not natural at all."

The arguments are passionate partly because trout are very sensitive to pollution and water temperature, making them the gold standard for clean water. "It's like the canary in the coal mine; they are an indicator species," said Hiemstra.

The fish need clean, cool water. In summer rainstorms, warm water can run too quickly into rivers, killing trout. So the fish are helped by anything that slows down runoff and lets water seep into the ground instead of swelling rivers.

Conversely, anything that doesn't easily absorb water — from pavement and driveways to rooftops — can send warm water into rivers.

Patton said there would be little problem if the DNR were content to have other fish in the Vermillion, just not the sensitive trout.

Dirk Peterson, the fisheries manager for the DNR's central region, which includes the Twin Cities, said developers could consider building narrower streets, bigger lots, smaller houses — anything to minimize "impermeable surface."

Hiemstra added: "It's not a lot more expensive. Depending on how it's done, it can even save (developers) money" because if water soaks into the ground, it could mean cost savings in gutters and sewers.

That statement left Remi Stone, public policy director of the Builders Association of the Twin Cities, flabbergasted.

"It surprises me that anyone would say that," Stone said. "The community inherits this land, goes out in good faith to develop it and, well, now we have trout.

"This absolutely makes houses cost more. It is always frustrating for them to change the rules in midgame."

Peterson admitted that retrofitting an existing development could be expensive — something that has happened in earlier battles over metro-area trout streams. But he said it was far cheaper to build new developments with the river water quality in mind. And he said it only affected building within about 100 feet of the river.

But Patton said the ruling would mean more sprawl: "You basically have a big swath of undevelopable land though Dakota County."

Downstream, there may be a far greater expense related to the designation.

The Empire Wastewater Treatment Plant is building a $50 million pipeline, partly to keep the river cool and trout-friendly, partly to protect the banks of the river from erosion during flooding.

Tim O'Donnell, communication specialist for the Metropolitan Council Environmental Services, which operates Empire plant, said the 13-mile pipeline is to divert wastewater from the plant into the Mississippi River in Rosemount, instead of the Vermillion River, where it goes now.

He said as the plant expands its capacity, the warm water will hurt the trout until the extension is completed.

About 25 miles of the Vermillion River and its tributaries, roughly between Lakeville and Farmington, already is designated a trout stream.

The new portion of river and tributaries totals 20.5 miles, including 12.5 miles on the Vermillion itself. It stretches from Highway 3 in Farmington to just east of Highway 52 in Vermillion Township.

Peterson asked: "How many major metropolitan areas have 200 lakes, three major rivers, and about a dozen trout streams? This adds to our overall quality of life."