During the summer months, Langstone Harbour, a eutrophic inlet on the south coast of England, is subject to blooms of green macroalgae commonly referred to as ‘green tides’. In a series of laboratory experiments, the vegetative growth of eight ‘green tide’ algae collected from the harbour was examined under a range of irradiances, temperatures, salinities and N and P concentrations. Test algae were Chaetomorpha linum, Cladophora dalmatica, Enteromorpha compressa, Enteromorpha linza, Percursaria percursa, Rhizoclonium tortuosum , Ulva curvata and Ulva rigida . All algae showed a broad tolerance to the environmental conditions of irradiance, temperature and salinity. The most rapid growth rates were recorded in irradiances ranging from 18 to 175 mmol m −2 s −1 , whilst the temperature promoting the most rapid algal growth ranged from 10 to 20 °C. With respect to salinity, the highest growth rates were recorded for algae cultured in the range 6.8 to 27.2 PSU. Several species were tolerant of salinities as low as 3.4 and 0 PSU. All algae showed a broad tolerance to a wide range of N and P concentrations. Maximum growth rates were recorded in nutrient concentrations ranging from 10 to 100 mmol m −3 PO 4 , 100 to 1000 mmol m −3 NO 3 and 60 to 100 mmol m −3 NH 4 . At these concentrations of N and P, considerable biomass was attained by the algae, with growth rates up to 21% per day. This, coupled with their broad environmental tolerance, is likely to promote their ecological success in the shallow, nutrient-enriched waters of Langstone Harbour and, indeed, in eutrophic waters worldwide.