Note: This story has been updated to include details of the damage to the Alameda County Water District dam.
The U.S. Environmental Protection Agency has launched an investigation into what authorities believe was an act of vandalism against a dam on Alameda Creek in Fremont.
The incident damaged an inflatable dam, leading to the loss of more than 150 acre-feet of water -- about 49 million gallons. That's enough to supply about 500 households for a year, the Alameda County Water District says. The agency serves about 340,000 people in Fremont, Newark and Union City.
The Fremont Police Department says it's investigating the May 21 incident and has increased patrols near the dam. The water district says it has beefed up security around its equipment.
Several large holes were found in the deflated dam, according to Fremont police spokeswoman Geneva Bosques.