Cities across the country want to make greater use of their urban waterways for recreation, but there's a problem: Much of the water is so polluted with manure that it may not be safe.

In Iowa, for instance, people are often reluctant to dip their hands in the Des Moines River, let alone to swim in it.

Most U.S. rivers are far cleaner than in decades past, but many still carry farm runoff and city sewage. That brings nitrates, ammonia and E.coli bacteria.

In Des Moines, officials are promoting an ambitious $117 million plan to attract kayakers.

Rick Tollakson is a developer who is leading the push. He says pollution concerns are overblown and that the proposed whitewater course will help attract younger people to the city.