A policeman and three villagers were killed in a gunfight between law enforcers and locals accused of illegally fishing on Lake Victoria, an official said Tuesday.
The lake, like many of East Africa's so-called Great Lakes, has been hard hit by overfishing, leading to increasing clashes between those plying its waters and authorities.
John Mongella, the governor of Mwanza region in northern Tanzania, told ITV Television a fight broke out between local fishermen and a police unit battling illegal fishing on Monday.
"Shots were fired, killing three villagers. The villagers then shot the person heading the patrol unit," said Mongella.
Tanzanian authorities have stepped up patrols on the lake.
Jumanne Muliro, police commander for the Mwanza region, said the police unit had seized nets used for illegal fishing on the island of Siza.
"The village chief called the owners of the nets who, upon arrival, attacked our unit," he said, adding police then opened fire.
Lake Victoria, which stretches into Kenya, Tanzania and Uganda and whose catchment also touches Burundi and Rwanda, is known for its unique biodiversity.
Last year, the International Union for Conservation of Nature (IUCN) warned that plant and animal life in Lake Victoria was being "decimated", with 20 percent of species facing extinction.
This was due to climate change, industrial and agricultural pollution, and poor fishing practices.
A report warned this could prove disastrous for lake communities.
Worldwide, overfishing is upending delicate ecosystems, but also impacting the livelihoods of millions.
In east Africa, conflict is growing over ever-scarcer lake resources.
Uganda has stepped up security on lakes Edward and Albert, which straddle the Democratic Republic of Congo whose fishermen increasingly venture into Ugandan waters due to depleted stocks on their side.