Abstract
With the environmental monitoring programmes at Horns Rev and Nysted Offshore Wind Farms coming to an end a pattern of the effects related to large-scale wind farms in a marine environment is starting to emerge. Being the first offshore wind farms of their sizes, it has been essential to map the effect on the environment with respect to future exploration potentials in Danish waters. Thus, an ambitious monitoring programme was launched to extract the actual effect that the construction of the wind farm would have on the environment from the potential effects predicted prior to construction. Horns Rev and Nysted Offshore Wind Farms, the two major Danish demonstration wind farms, have been the subject of a long and unbroken line of surveys. Ongoing environmental monitoring has been performed since the Environmental Impact Assessment (EIA) in 1999 and the baseline studies before erection of the wind farms in 2002-2003. The programmes will continue until the end of 2005, thus the environmental monitoring programme has gathered the most extensive existing dataset on the disturbance effects related to large-scale offshore wind farms. The PSO-funded Danish monitoring programme includes issues such as benthic flora & fauna, introduction of hard substrate habitat, fish, marine mammals and birds.