Authorities are trying to determine what caused tens of thousands of fish to turn up dead in the waters off Marina del Rey over the weekend.

Updated Article: Algae Bloom Might Be Behind Dead Fish

The first report came in just after 9 p.m. Saturday at the A-Basin in the 13000 block of Tahiti Way, officials said. When Los Angeles County Sheriff's Department deputies arrived, they discovered an estimated 70,000 dead anchovies floating in the water, along with other sea life, including sting rays and angel sharks.

It was not immediately known what caused the fish to die and wash up to the basin. A bait fish expert told NBC4 that Saturday night’s low tide combined with low oxygen levels may have been the cause of the massive die off.

"Inside the marina here you have the sea walls that make it a confined space, so there's only a certain amount of oxygen in the water immediate to the fish," said bait expert Mike Spears. "It was a low tide, which means the water was going out, nothing was coming in from the ocean, so it was just stale water and they just suffocated in it, and everything around them suffocated, too."

Matthew King of Heal the Bay said the weather may be to blame.

"Warmer temperatures can create algal blooms, which will suck up a lot of oxygen," King said. "That's happened in the past, and hot weather always has been associated with low oxygen levels in the water."

On Sunday afternoon, workers hauled away about 175 garbage bags worth of fish, weighing an estimated 7,000 pounds.

A similar die-off took place in Redondo Beach in 2011 when 35 tons of dead fish surfaced in King Harbor.

Andrew Lopez contributed to this report.