Gov. Mark Dayton has denied a request by 30 environmental and conservation organizations to consider a plan for a smaller bridge on the St. Croix River.

In a letter sent Monday, the Minnesota Environmental Partnership and several other groups argued that Minnesota would save millions of dollars by backing away from the proposed $690 million bridge project in favor of a smaller, less-costly plan.

But Dayton, who this spring declared his support of the current proposal for a four-lane bridge at Oak Park Heights, won't be ordering a review.

"We are in the final stages of securing funding for the current plan for the [bridge] project, and all parties are working to finalize this as soon as possible," Dayton spokeswoman Katharine Tinucci said Tuesday.

The environmental organizations wrote that legislation in Congress to permit construction of the bigger bridge "would set a damaging national precedent" for the St. Croix and other rivers protected under the federal Wild and Scenic Rivers Act.

The current proposal would build a freeway-style bridge at Oak Park Heights to replace the 80-year-old Stillwater Lift Bridge. Bills by Rep. Michele Bachmann, R-Minn., and Sen. Amy Klobuchar, D-Minn., seek to exempt the new bridge from federal law, clearing the way for construction.

Supporters have said the bigger bridge would have sufficient capacity for future traffic growth. Part of the plan involves looping a pedestrian and cycling trail over the Lift Bridge once it's closed to vehicle traffic. Supporters say the current proposal is the least harmful of several plans that were considered over the past two decades.

Opponents say the proposed bridge is too costly, would invite urban sprawl, and its size would overwhelm the scenic river.

The letter asked Dayton to order the Minnesota Department of Transportation to "fully evaluate" the alternative design of a smaller three-lane bridge that would cross the river diagonally from just south of downtown Stillwater to where the Lift Bridge connects with Wisconsin.

That bridge would have slower speeds, would be built lower to the water, and would cost less than half of the current proposal, supporters have said.

The group that earlier this summer unveiled the alternative plan, Sensible Stillwater Bridge partnership, didn't sign the letter to Dayton. However, spokesman Peter Gove said earlier that his group has been trying to arrange a meeting with MnDOT chief Tom Sorel to discuss the alternative plan.

Kevin Giles • 651-735-3342 Twitter: @stribgiles