Submergent macrophytes: growth under winter ice cover.

Densities of 26 submergent macrophyte species were determined in situ regularly for 3 years by individuals using self-contained underwater breathing apparatus (scuba). Although most of these species grew only during the summer, ten maintained high population densities and productivity throughout the winter. Maximum winter photosynthetic activity was 10 to 20 percent of summer rates. Extensive productivity of submergent aquatic plants under winter ice cover has not been well documented.