According to LongSwims Database the Catalina Channel is one of the most historically significant and consistently popular marathon swims in the world and was first swum solo by George Young in January 1927. It is part of both the Triple Crown of Open Water Swimming and the Oceans Seven.
The Catalina Channel (technically San Pedro Channel) separates Santa Catalina Island from the Southern California mainland. The minimum distance across the channel is 19.6 statute miles (31.6 km), between Arrow Point on the island and Long Point, Rancho Palos Verdes. Swimmers typically start from the beach at Doctor's Cove for a slightly longer swim of 20 miles.
Solo and relay swims are sanctioned by the Catalina Channel Swimming Federation (founded 1981).
More info at https://swimcatalina.org/swim-successes/