The melting of a deep Sierra Nevada snowpack is turning recreational rivers into rampaging torrents that have killed 11 rafters in three weeks.

"The waters are high and fast," said David Johnson, spokesman for the state Department of Boating and Waterways.Most of the deaths involved people rafting without professional guides. Two involved commercial rafters. The toll also included two boys who used air mattresses.

The big melt is happening just as the vacation season is getting under way, and rafting has become a popular summertime activity on California's rivers.