LA FARGE, Wis. (AP) — A manure spill in southwest Wisconsin could have long-term impacts on a popular trout stream.

Wisconsin Department of Natural Resources officials told Wisconsin Public Radio that last week's spill killed more than 1,100 fish in Otter Creek, including brook and brown trout.

Bacteria in the stream that digest the manure also use oxygen in the water, said David Rowe, the department's fisheries team supervisor in Fitchburg. The low oxygen level quickly kills the fish. Ammonia in the manure can also kill fish.

Rowe estimates that his nine-county region sees about seven manure spills annually.

It can take years for oxygen levels to return to normal after a manure spill, said Jeff Hastings, the project manager of Trout Unlimited's Driftless Restoration Project, which works to restore trout habitats in southwestern Wisconsin.

"Your most productive fish will likely be killed in such an event," Hastings said. "These populations have to self-regenerate, some fish will survive and will start repopulating but it takes time.

Ole Yttri, clerk for the Town of Webster, said he hopes the manure spill won't have a big impact on other waterways in the area.

"We had a lot of rain last week also, 3 to 4 inches of rain in this area, so I would think this would help dilute the water system," Yttri said.

Trout fishing brought in more than $1.6 billion dollars of tourism revenue to southwestern Wisconsin and neighboring states last year, according to a study by Trout Unlimited.

Department officials say the cause of the spill is being investigated.