not sure exactly where but i think its "friends of castaic" that run most the events at the lake im sure castaic lake is on facebook, or the friends of castaic. they do have a calendar on the castaic website though maybe there. i think its only once a year but you can call and check also.
Friends of Castaic organize the event, more information is available on the Castaic website calendar, and Facebook page. It was a great event, the kids had a blast, got lots of swag including a tackle box with terminal tackle, trout bait, etc.