While sea kayaks were originally designed for use on the ocean, they are at home on any large body of water or in situations where you want move efficiently for a long distance. Sea kayaks are the nearest ancestor of the original kayaks created by the Inuit and Aleut peoples of the Arctic. These original kayaks were often quite narrow and fairly long. This help them move efficiently through the water even when the wind blows and the waves get large. This makes them well suited for any body of water where the conditions may get rough or if you just want to be able to go a long distance with a minimum of effort. Sea kayaks are typically designed with a cockpit small enough to accept a spray skirt. This helps keep water out of the cockpit. They also often are equipped with bulkheads that provide additional safety and a dry place for storing lunch or camping gear. Due to their length sea kayaks are typically heavier than recreational kayak. The length also makes them less maneuverable for investigating small coves and streams. They will not be as responsive as a whitewater boat when attempting to navigate fast moving water.
I'll be in Madison, WI for this big paddle sports show. Come say "Hi"!