You unlocked another plant to deal with those zombies in water, specifically the annoying ones such as Surfer Zombie, Octo Zombie and Fisherman Zombie for just 25 sun, it's like a Potato-mine but it doesn't take 14 seconds to attack unlike Potato-mine, it's the Tangle Kelp!

Welcome to the depths of hell, and when I say hell, you and I both know we're talking about the Big Wave Beach...