Oroville – Foam floated downstream and made circles on the water last week in the pool below Oroville Dam.

Water quality experts are trying to determine why.

Foam can happen naturally, or it can be a result of something else in the water. At this point the cause of the foam is unknown. Water tests were planned Wednesday, with lab results available in about two weeks, said Bryan Smith, supervising engineer with the Central Valley Regional Water Quality Control Board.

The state Department of Water Resources took photographs of the foam last Thursday in the Diversion Pool, which is where the Feather River begins below the dam as water comes out of the spillway or the Hyatt Powerhouse. Enterprise-Record photographer Bill Husa took photographs the next day, after a resident in the area called the newspaper to report the foam.

Water is being released from both the damaged spillway and the powerhouse as dredging work continues at the base of the spillway.

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Water samples in the Diversion Pool to test for substances are not routinely done, Smith explained. Tests for other things, such as turbidity and water temperature, are conducted several times a day when dredging is taking place, Smith said. The last time that was done was Thursday, the day DWR took photos of the foam. Those samples are done along the shore.

Smith said he received photos of the foam from DWR Monday afternoon.

It might be “foaming agents” in the water, or natural causes might be found. Smith said decaying plants and algae can cause foam in water, or a change in water temperature. Pollen can also appear like foam, he said.