The inshore lifeboat was launched after a man was seen in the water off Brooklands Pleasure Park, East Worthing.
The man had gone into the water to recover what he believed to be a canoe. Despite the shallow water, his wife was concerned for his safety and called the coastguard.
The lifeboat reached the scene in about 15 minutes but the crew found the canoe was in fact a sailing racing marker snagged on the groyne.
The man had come out of the water and was ashore. The lifeboat was stood down and returned to station.