Oil spills do occur in freshwater but are usually more localised.
Examples include Torrey Canyon, which ran aground off the coast of Cornwall in 1967 after the captain ignored charts showing submerged rocks. The tanker lost half it's cargo of oil and a spill of 120,000 tonnes of crude oil covered the beaches of the south coast and France and killed over 100,000 birds, particularly Guillemots. The worst to date was the Amico Cadiz which ran aground off Brittany and lost 227,000 tonnes. In 1989 the Exxon Valdez incident released 40,000 tonnes of oil and caused an oil slick that covered two thousand six hundred square miles. When the tanker the Braer ran aground off the Shetland islands in 1993 winter 85 tonnes of oil were spilt killing 700 sea birds.