It’s been a long winter.

No one knows this better than Hugh Valiant, manager of the Department of Natural Resources Waterville Fish Hatchery.

“On a positive note, this has been one of the better years for good ice,” he said. “Logistically, anglers have been able to move around on area lakes easily and safely.”

On the downside, the ice and snow that arrived very early in December have created potential problems for some lakes prone to winterkill.

Winterkill occurs when ice and snow block out sunlight, shutting down the photosynthetic process in submerged plants, causing dissolved oxygen levels to fall to levels insufficient to support fish life. Typically, shallow lakes are the most at risk to experiencing winterkill.

Fisheries personnel regularly monitor O2 levels on area lakes to determine downward trends that might indicate a lake is headed for a crash.

“It’s been a long winter and there has been some downward trends in some lakes,” Valiant said. So far, four lakes in the area — Dora and Pepin in Le Sueur County, and Phelps and Union Lakes in Rice County — have been open to liberalized fishing regulations because of low O2 levels.”

Liberalized fishing regulations mean that anglers can use a variety of methods to harvest as many fish as they can without regard to limits on lakes where winterkill is imminent.

Other lakes that have not yet been open to liberalized fishing but are falling to dangerously low levels include Lilly Lake, Eagle Lake and Circle Lake.

Valiant said that most area lakes equipped with operating aeration systems, designed to create open areas to allow oxygenation of the water, seem to be maintaining sufficient O2 levels.

Area lakes equipped with such systems — Loon, Crystal, Mills, Elysian, Lura, Ida, Albert Lea and Scotch lakes — seem to be holding their own.

Whether a lake suffers winterkill can depend on a variety of factors, including water levels and existing vegetation.

Valiant also said that a winterkill on shallow lakes isn’t always a bad thing since a total winterkill in a lake makes it a perfect habitat for rearing walleye fry.

While many lakes appear to be able to weather the prolonged winter conditions, Valiant said some warmer weather to create an inflow of fresh water will be critical in upcoming weeks.