Though, the first session doesn't start until June 2nd you can start getting tickets to kayak the LA River. A strange experience that reminds us that we did in fact concrete a river in Los Angeles. You'll be headed down the Sepulveda Basin Wildlife Reserve section of the river and actually see some greenery. Or, you could try the harder section and go down the Glendale Narrows.
There are two sites that"ll get you in the water and they"ll both provide you with the kayaks and gear you need as well as someone to guide you.
LA River Expeditions
LA River Kayak Safari
*This site may need to be updated, check their social media