Wildlife officials are trying to determine the cause of a fish die-off in a Northern California lake, which came just a couple weeks after an earlier mass death elsewhere in the state.

Hundreds of dead carp have lined the shores of Lake Mendocino, about 10 miles northeast of Ukiah, the first being reported Sunday.

State fish and wildlife biologists were called in to investigate but remain puzzled over what caused it.

Los Angeles County cleanup crews begin the massive cleanup of thousands of dead fish at Marina Del Rey, Monday, May 19, 2014. Marine biologists worked to determine whether a recent Southern California heat wave, lack of oxygen in the water, or other factors may have caused the fish die-off in coastal waters near Los Angeles. Over the weekend thousands of dead anchovies, stingrays and even an octopus died and floated up onto the coastal waters creating a 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. (AP/Nick Ut )

Los Angeles County cleanup crews begin the massive cleanup of thousands of dead fish at Marina Del Rey, Monday, May 19, 2014. Marine biologists worked to determine whether a recent Southern California heat wave, lack of oxygen in the water, or other factors may have caused the fish die-off in coastal waters near Los Angeles. Even more recently, a carp die off in Lake Mendocino is puzzling scientists as well.  (AP/Nick Ut )

U.S. Army Corps of Engineers spokesman Ryan McClymont told the Press Democrat of Santa Rosa that the water doesn’t appear to be too warm or lack oxygen since the die-off is affecting only carp, not other fish. He said the fish are resilient, but there are some diseases that affect only carp.

“Right now, we’re just in limbo,” McClymont told the newspaper.

The discovery follows a fish die-off this month in a Southern California harbor.

A gull scoops up dead fish from the water at Marina Del Rey Monday, May 19, 2014. Marine biologists worked to determine whether a recent Southern California heat wave, lack of oxygen in the water, or other factors may have caused the fish die-off in coastal waters near Los Angeles. Over the weekend thousands of dead anchovies, stingrays and even an octopus died and floated up onto the coastal waters creating a 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. (AP/Nick Ut )

A gull scoops up dead fish from the water at Marina Del Rey Monday, May 19, 2014. The dead anchovies, stingrays and even an octopus died and floated up onto the coastal waters creating a silvery blanket of fish on the water’s surface, creating a pungent smell and set off a feeding frenzy of harbor seals, pelicans and seagulls. (AP/Nick Ut )

Tens of thousands of northern anchovies were found dead along the coastal waters of Marina del Rey. State authorities said the cause was too little oxygen.

Check out photos of the Lake Mendocino die off in the Press Democrat’s report.

The Associated Press contributed to this report.

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