About 3,300 plants were recovered in the raid, which was conducted at about 4 a.m. at an area between Castro Valley and San Ramon, police said.

The growing operation had been found earlier during routine park patrols. An elaborate irrigation system tapped into the park's water supply was watering the plants.

Grow operations are of particular concern to the park district since the suspects remove areas of native vegetation and use fertilizer, poisons and pesticides around the marijuana plants, according to police.

The plants were taken to an undisclosed location and destroyed.

Anyone with information about the growing operation is asked to East Bay Regional Parks Police at (510) 881-1833.