The company that built and operates the Carlsbad seawater desalination plant took over stewardship of the Agua Hedionda Lagoon this week, the only San Diego County lagoon that allows power boats, kayaks, paddleboards and other recreational and commercial activities. Poseidon Water will be responsible for dredging Agua Hedionda to keep it open and deep enough for public and private uses including a YMCA Aquatic Park, the Hubbs-SeaWorld Fish Hatchery, the Carlsbad Aquafarm shellfish operation and the lagoon foundation’s nature center.