ROCHESTER, Minn. -- Minnesota Health officials have warned all lake swimmers to keep their nose out of the water or risk contracting a "brain-eating amoeba."

"Given that we've seen prolonged periods of warmer weather, I wanted to bring to your attention the risk of naegleria fowleri infection," said state director of infectious disease Kris Ehresmann in a Friday, July 10, afternoon news call.

Ehresmann said cases have not been reported from Minnesota waters this year, but that "swimmers should assume that naegleria is present in fresh water."

Health officials say the concern stems from the recent stretch of unseasonably warm weather in the state.

The infection, which is rare, was formerly limited to lakes in the southern U.S. Ehresmann said that recent years have seen infections in the northern states following prolonged periods of very warm temperatures, "which results in higher water temperatures, and lower water levels."

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There is no treatment, and the illness that causes neurological symptoms can be deadly. Many people have antibodies for the infection, however, which suggests that some people can fight it off.

Health officials advise swimmers to "keep your head out of the water, hold your nose shut or keep your nose shut using nose clips when going under water." They also advised avoiding the digging in or stirring up sediment.

Diving and water skiing -- any sports that force water up the nose -- increase the risk of naegleria fowleri.