Although now officially frozen over, this photograph of the Riverdale bluffs area shows extensive open water on Lake Sakakawea on Jan. 13. Lake Sakakawea was declared frozen on Jan. 24, the latest date in history.

An all too typical winter in North Dakota is when snow piles up on lakes already covered by a thick ice pack, so much so that ice anglers need to use extensions on their augers to punch through two to three feet of ice. Sometimes freeze-up comes early in the winter season too, adding days and weeks to a long season and threatening the dissolved oxygen content vital to life under the ice. Winter kills of fish often follows.

This winter, though, has been anything but typical. Many lakes that did freeze over early in the winter season later opened up, entirely or partially, in warm weather and high winds, only to freeze up again as temperatures approached more seasonal levels.

What are the possible effects of open water during part of the winter season, and minimal ice cover, on fish? Here’s Scott Gangle’s response to that question. Gangle is section leader for the North Dakota Game and Fish Department’s fisheries division.

“We usually have concerns with winter kill and dissolved oxygen in a normal winter,” said Gangle. “In a winter like this it can make a huge positive difference. This season has been just beautiful from the start to now, very little snow and ice. It should be a positive.”

The state’s largest body of water, Lake Sakakawea, wasn’t declared frozen over until Jan. 24, the latest such declaration in the history of that reservoir. A mid- to late December freeze for Sakakawea is common. The late freeze meant an extra month of open water that links to oxygen above.

While Sakakawea is a vast and deep body of water where oxygen levels during the winter months raise little concern, that is not the case on many of North Dakota’s lakes.

“Many fishermen are familiar with long winters, early ice up, lots of snow,” said Randy Hiltner, NDGFD northeast fisheries district supervisor in Devils Lake. “That kind of winter correlates with a fish kill later on, but this is the winter of the opposite so far.”

Temperatures are generally colder than most of the rest of the state in the Northeast Fisheries District which extends all the way to the Canadian border. Ice often gets very thick. However, this year a lack of heavy snow cover is proving to be an added benefit to many small lakes.

“There’s more sunlight getting through and in many places clear, blue ice or thin ice,” explained Hiltner.

Sunlight penetrating through ice enables plants to grow and produce oxygen. It is when plants die that a lake becomes particularly susceptible to low oxygen levels.

“Generally, we have ice but not as thick as typically this time of year,” added Todd Caspers, NDGFD fisheries biologist, Devils Lake.

When asked about dissolved oxygen levels, Caspers explained that once a lake is frozen over you are “stuck with whatever you’ve got.” Sometimes, given the right conditions and length of winter, oxygen levels underneath the ice will fall to levels lower than necessary to sustain life.

This winter has been anything but normal. However, while ice thickness has been somewhat less than usual, it has generally been sufficient enough for ice fishermen to pursue their passion, albeit with perhaps a bit more caution than in most years.

Caution is what led the Devils Lake Volunteer Fire Department to cancel their annual ice fishing derby, the largest in the state, for the first time in 37 years. While ice anglers have been drilling holes and catching fish for several weeks on that body of water, it was determined that putting 5,000-6,000 fishermen in one area of the lake was not prudent.

In the southwest area of the state, sometimes referred to as the “Banana Belt” because of the frequency of warmer temperatures than the rest of North Dakota, lakes that were frozen opened up during a recent warm spell before freezing once again. One of those bodies of water was Patterson Reservoir near Dickinson.

“I’m assuming other lakes opened up a bit too,” said Jeffrey Hendrickson, NDGFD western fisheries district supervisor. “It means people should be very careful when they are going fishing. I would say there’s not much left of the ice fishing season.”

Hendrickson noted the lack of snow cover on district lakes in the western part of the state, saying it was beneficial to fish populations.

“As long as the ice is clear the sun can enter and photosynthesis produces oxygen,” said Hendrickson. “When lakes are froze over they cannot exchange oxygen with the air. Usually the end of January to the end of February is the critical time.”

Hendrickson added that lakes in his district froze over about a month to a month and half later than usual which lessens the chance of winterkill.

At Lake Darling, located northwest of Minot, several areas of previously frozen water opened up during a warm and windy period, then froze again recently as temperatures dropped. Upper Souris National Wildlife Refuge Manager Tom Pabian called the situation there “concerning”, and reminded all ice fishermen to exercise caution.