Mosses are generally considered to be land plants although a few species are found growing submerged in streams and shallow areas of lakes. But there is now increasing evidence that certain species are able to grow successfully in deep water, often forming the dominant vegetation1,2. We have made the first underwater observations on deep-water mosses growing in Antarctic lakes. A SCUBA diving survey was carried out on Signy Island, South Orkney Islands (60° 43′ S, 45° 38′ W) in 1971 and 1972.