Initial testing shows no water contamination or other toxins. State biologists are running tests on a dozen dead fish from the Redondo Beach Harbor to determine the cause of a massive die-off Tuesday.

Millions of dead of sardines were discovered in the Redondo Beach harbor Tuesday morning, initially raising concerns about possible water contamination. Water samples tested on-site Tuesday were clear of contamination, but California Department of Fish and Game (DFG) wardens collected about a dozen dead fish to send via overnight mail to the DFG laboratory in Rancho Cordova, where biologists will run tests to confirm that the die-off was not due to toxins in the water.

Because all the dead fish were contained in one area of the harbor, officials believe that the most likely culprit was oxygen deprivation. Recent storms could have caused the school of sardines to swim around the breakwater and into the enclosed harbor, where they were trapped and unable to get out before depleting the water of oxygen.

Although this is not a common occurrence, biologists say that it can happen under certain conditions.

The city of Redondo Beach activated its crisis response team Tuesday and by noon, more than 50 volunteers were scooping fish with nets. The dead fish were transported to a collection center, where they will be recycled into fertilizer. The harbor remained open throughout the day and continues to remain open.

Biologists at the northern California laboratory expect to complete their testing by early next week, and DFG wardens will continue to monitor the harbor.