Of course a fishing community such as this has opportunities for visitors to try their luck too. You can fish straight from the cliffs or go on boat trips. Two to three hours will set you back around SEK 300 for ordinary fishing and for more money, you get to fish crab and lobster too depending on season. Vinga Båt och Fisketurer at Fotö or Klova harbour is one alternative (see e-mail under "other") and another one is Anders Båtturer (see link) which also offers seal safaris.
Swimming is obviously a major thing on an island and you can find your own cliff to sunbathe and swim from anywhere. Just make sure you check the depth before diving in head first. If you have children or just prefer beaches, there are several places to head for: Röd, Lappesand and Hästen are the most well-known and you will find them signposted and shown on maps.
Hönö is a bit of a diving centre for those in the Gothenburg area. See the link below for the main company to contact in Klova Harbour.
Equipment: You can rent it from Oxygene (see link).