What do you get when you dump about 140 truckloads of rock into a river? You get a rock dam, of course. That’s what Hutchinson residents now see when they cross the Crow River bridge.

The $1.2 million dam is made up of more than 9,000 tons of rocks and boulders arranged in eight tiers called weirs. It was completed in late 2007. Landscaping of the small parks on either shores will take place this year.

“Relatively, it is a pretty simple project,” City Engineer Kent Exner said in October. “The art is in placing the rock to maintain flow.” Once water begins flowing over the dam this spring, workers with Park Construction of Hampton will be able to see if some rocks need to be adjusted to improve flow.

The city’s old concrete dam, which included a pair of adjustable tainter gates, was starting to show its age. Cracks were observed in the face of the dam, and the gates were difficult to maintain.

A benefit of the new dam is that in many flow situations fish will be able to navigate their way upstream. The old dam was a one-way passage — fish could tumble over it to go downstream, but there was no reversing course to go upstream.

Park Construction has worked on several natural rock ladder dams, including one near Owatonna and another on a tributary to the Red River of the North. The dam was designed with the assistance of the Minnesota Department of Natural Resources, which also contributed a $475,000 grant to the project cost. The city paid the rest.