LOWER RED LAKE — Red Lake Nation tribal scientists are checking the waters of Lower Red Lake frequently for the appearance of zebra mussels that have already invaded the Upper Red.

They’re worried that the destructive creatures will spread quickly and threaten a fishery that produces 1 million pounds of walleye per year.

Zebra mussels have turned up in hundreds of Minnesota lakes and rivers since they first appeared in Duluth harbor in the ballast waters of an oceangoing ship. It’s not clear how much zebra mussels will affect Red Lake, but it’s not likely to be good. Zebra mussels can crowd out native mussels and filter out massive amounts of algae — the food that drives the walleye fishery.

“A lake can only support so much biomass,” said Shane Bowe, the tribe’s water resources director. “If the zebra mussels start at the bottom of the food chain and replace a million pounds of biomass with themselves, that’s our whole walleye harvest.”

Lower Red is the largest body of water in Minnesota, and only tribal members are allowed to fish it. It’s completely contained within the reservation, but connected to Upper Red by a mile-wide strip of water. And the tribe only partially controls the Upper Red. That lakes’ east side is lined with cabins and resorts owned by non-tribal members.

Some Red Lakers see the problem as a failure by people outside the reservation to keep zebra mussels out. Minnesota Public Radio News reports that the young zebra mussels came in via boats used by non-tribal members accessing the eastern part of Upper Red — which the tribe doesn’t control.

Tribal secretary Sam Strong said mussels could put 500 fishery jobs at risk.

“This is our storehouse,” he said. “It’s woven into our way of life. The lake is like one of our relatives. It’s hard to watch your brother or sister or mother getting poisoned. That’s how I see it. That’s how a lot of us see it. When the lake comes under attack we all feel the pain.”

Strong blames the fishery managers in charge of Upper Red Lake. He says there weren’t enough invasive species inspectors to keep boats from bringing in the zebra mussels.

“It’s just the same story we’ve heard for centuries,” Strong said. “The neglect of our resources.”

There are three public boat launches on Upper Red Lakes. Minnesota Public Radio News reports only two are ever staffed by boat inspectors, and only for a few days a week during the busiest time of the year.

The state pays $10 million a year to counties to build their own boat inspection programs.