How seriously are people in authority taking the spread of quagga and zebra mussels? Seriously enough to risk angering thousands of anglers. Judging that the risk of hurt feelings will be more acceptable than the possibility of losing its water-delivery system, the Casitas Municipal Water Board voted for a one-year ban on private boats on Lake Casitas -- one of the state's most popular bass lakes. Quagga and zebra mussels attach to the hulls of boats and are spread as boat owners try different lakes. Having done billions of dollars in damage in the Great Lakes region, the mussels arrived in Southern California in 2007. In January, zebra mussels were found in a reservoir near Hollister. That is prompting pre-emptive actions by water agencies statewide. Unfortunately, keeping mussels out of lakes and reservoirs usually means forbidding most boats. More than 30,000 boats launch at Lake Casistas each year and the proposal to ban them angered the 300 who attended the Casitas meeting, wrote the Ventura County Star. Some out-of-town observers were concerned that other agencies across the state are taking similar actions. Charged with supplying water to customers and residents, directors of local water agencies are realizing that keeping the mussels out of their lakes is a higher priority than letting recreational boaters in. It's not a popular position, but necessary.