The fish stock of rainbow trout in Yellow Lake along Highway 3A has dwindled since the winter, provincial officials said.
The ministry responsible said a "significant but incomplete" winter kill is presumed to have happened in the popular fishing lake.
"Test netting last week found only small rainbows that would have been stocked as yearlings last spring. This is typical of a partial winter kill event in that large bodied fish are the first to succumb to depleted oxygen levels," the province said in a statement.
The lake will be replenished with about 5,000 "catchable-sized" rainbow trout in the coming days.
The province noted there's no indication a mudslide in April affected the lake's fish stock, which sent tonnes of mud and debris across the highway and into Yellow Lake.
Yellow Lake is stocked annually with Kokanee and trout by the Freshwater Fisheries Society of B.C.
It's unclear if the population of Kokanee in the lake has been impacted, the province added.