DEVILS LAKE (AP) - State officials are trying to find out how adult minnows got into the open channel below the Devils Lake outlet's rock-and-gravel filter system.

"I just don't understand how these fish could have swum through many hurdles and still survive without a scratch or any mark on them," state water quality director Dennis Fewless said.

The filter is supposed to prevent the transfer of adult fish and other smaller organisms. Manitoba officials worry those organisms will get into their water system.

The outlet involves 14 miles of pipeline and open channel that drains water from the flooded lake into the Sheyenne River, which flows into the north-moving Red River. This year, the outlet started operating last week.

Bill Delmore, the North Dakota attorney representing the Manitoba government and outlet opponents, e-mailed photos to state officials last week showing adult minnows in the open channel. He demanded the outlet operation stop, saying the fish were a violation of the outlet permit.

North Dakota biologists surveyed the open channel area Wednesday to investigate the claims.

Fewless said that to get through the filter, the fish first would have to get through an intake, a screen inside the intake, then pumps and a piping system.

"If it is proved that these fish passed through the filter, then we will take additional actions such as putting in additional screening systems," Fewless said. "But at this point, it is too early even for speculation. We are planning to send a diver to check the screen."

Fewless said the research will take some time, and he has no plans to stop the outlet.

"We take this matter seriously, and we are doing our best to evaluate the situation as thoroughly and fairly as possible," he said.

Fewless' Manitoba counterpart, in a letter to Fewless, said the State Water Commission should "immediately cease operation of the Devils Lake outlet until the matter is thoroughly investigated and remedial measures are implemented."

Dwight Williamson, director of the Water Science and Management Branch of Manitoba, said the current permit specifically says "the intake must be fitted with a screen system of sufficient mesh and size to preclude the uptake or transfer of adult fish species."

If fish get through the filter system, it is a violation of the permit requirement, he said.

During the 11-day operation of the outlet in 2005, small fish and freshwater shrimp were spotted in the same area, Williamson said. The upper layer of the gravel part of the filter was not strong enough, and the state Health Department ordered more metal screening to improve the filter, which was installed earlier this year, Williamson said.