Swimming is the act of moving through the water by using your arms, legs and body. The most common reason for swimming in Kailua Bay is recreational. There are many types of water activities that take place in the bay so several bouys have been placed offshore for the stretch of beach that fronts the park to designated a swim area only. The waters of Kailua Bay are generally protected from large surf because of the outer reef that straddles the length of the bay.

Onshore winds are consistent in the bay and can bring portuguese man-o-war (stinging blue jellyfish) that cause a painful sting. Lifeguards will typically post a sign to warn swimmers. There is also stinging limu which causes a blistering rash. The seaweed fragments can get caught in swimwear and rub aaginst the skin releasing the toxins. The Health Department will issue public warnings when there are outbreaks of the rash in swimmers.

During heavy rains the bay has been closed to swimmers and water activities because of polluted runoff that is emptied into the bay through Kaelepulu Stream, Oneawa Canal and the large storm drains in the residential area of Lanikai. Signs are posted until it is safe to swim in the water.