Huge fish die-offs in California and Minnesota. What's happening?

Huge fish die-offs in the waters off California and in a lake in Minnesota may be caused by the same thing: lack of oxygen. But oxygen deprivation was brought on by different sources.

A lack oxygen in the water brought on by the recent Southern California heat wave is one of the reasons experts are suggesting for a huge fish die-off in the waters of Marina Del Rey.

California Fish and Wildlife workers are still scooping dead sea life from the surface of the harbor Monday after thousands of dead anchovies, stingrays and even an octopus died and floated up over the weekend.

The silvery blanket of fish on the water's surface created a pungent smell and set off a feeding frenzy of harbor seals, pelicans and seagulls.

Marine biologists were working Monday to determine the cause, with some suggesting the recent heat wave was to blame.

Similar fish die-offs occurred in Redondo Beach and the Ventura Harbor in 2011.

Meanwhile, in Minnesota, researchers say that last winter's heavy snowfall is partly to blame for a fish kill that took out tens of thousands of walleye, bass, northern pike and other species on Grand Lake near Duluth.

Dan Wilfond, Department of Natural Resources fisheries specialist for the Duluth area, said even bullhead were among the species affected — an indicator that the fish kill was fairly severe. He estimates roughly 35,000 fish died.

Wilfond said the 1,600-acre Grand Lake is somewhat susceptible to winter fish kills and its oxygen concentrations are monitored annually. That said, the lake hasn't had a severe winter kill documented since the 1950s.

He said heavy snow cover contributed to the die-off, because thick snow lets less light into the lake and aquatic plants can't produce oxygen.

"It's a pretty popular lake in the area ... so residents and local anglers are certainly going to be very disappointed about this," he said.

Because of the kill, the DNR is going to stock walleye in Grand Lake over the next three years.

"We anticipate in a few years there will be some pretty good fishing out there, particularly for walleye," he said.

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