Fish die-offs limited as water temperatures rise

By Joe Albert Staff Writer

Duluth, Minn. – In 1983, Lake Bemidji experienced a massive
die-off of tullibees, with a total kill of about a quarter-million
fish.

Given the heat that’s encompassed the state of late – and that
began with a sweltering Memorial Day weekend – officials were
concerned such an event could happen again.

‘We were getting a little nervous,’ said Dennis Johnson,
assistant area fisheries manager for the DNR in Bemidji. ‘We were
thinking we were getting close.’

Alas, there hadn’t been any tullibee die-off when Johnson
checked the lake on Tuesday, and he hadn’t heard of any other
problems in the area. However, rivers and streams were running low
and heating up.

That seems to be the story around the state. Many areas have
water that’s hovering on the brink of too warm, but it hasn’t
tipped yet. Any fish kills have been small and limited in
scope.

Streams in the Duluth area are an exception, where the heat and
lack of rainfall has proved to be a toxic mix in some streams.

‘You certainly don’t like to see conditions like this because
you tend to lose some fish in certain places,’ said Deserae
Hendrickson, DNR area fisheries supervisor in Duluth. ‘We
definitely have had fairly low water levels for a couple of weeks
now.’

Low water levels, in trout streams in particular, cause problems
because the water warms up faster than would be typical. The Knife
River near Duluth, for example, on July 10 had a flow rate of 5.5
cubic feet per second. The typical rate at that time is more than
20 cubic feet per second, Hendrickson said.

‘That is kind of the relative difference (in other streams) we
are seeing based on the long-term averages for this time of year,’
she said.

The low water and heat combination did cause a fish kill in the
Lester River near Duluth.

Conservation officers received a TIP call that juvenile
steelhead were being taken from the river. When they arrived, there
were about 15 fish on the bank, which apparently had been picked up
by kids swimming in the area, according to CO Chris Johnson.

Hendrickson said her office was called to the Lester River kill,
and that 35 rainbow and Kamloops trout were dead. The water
temperatures in the river were about 84 degrees; the optimal
temperature for trout is below 70 degrees, she said.

Any fish that didn’t migrate downstream to Lake Superior might
have succumbed to the heat, Hendrickson said.

‘It isn’t surprising the fish were dying at that point,’ she
said.

The trout lakes in the area hadn’t experienced any kills, but
there was getting to be a ‘pretty narrow margin’ where the water
was cool enough and there was enough oxygen, Hendrickson said.

Bob Davis, area fisheries manager in the Windom area, said he
hadn’t heard of any problems with fish, and said water levels in
lakes and rivers were coming back down to normal levels.

‘We had a lot of rain earlier in the year, so things were up,’
he said. ‘We had high flows in the rivers and really high lake
levels; now, through evaporation, things are coming back to
normal.’

Still, moisture is needed in the area, Davis said.

Earlier this week, Dave Zappetillo, DNR area fisheries
supervisor in the east metro, said he had calls about two fish
kills in shallow, small, private ponds that involved walleyes and
sunfish.

He wasn’t concerned yet about fish kills in the larger lakes,
but said walleye rearing ponds, which are similar to the lakes
where kills occurred, could be harmed.

‘It may have a long-term effect on our walleye ponds,’
Zappetillo said.

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