Within the EU, an Environmental Impact Assessment  (EIA) must be carried out before public approval for larger projects can be granted. The minimum requirements of the EIA are specified in the EC Council Directive 85/337/EEC [i] amended in Directive 97/11/EC [ii].
The directives require that private and public projects, which are likely to have significant effects on the environment, must be subject to an assessment of their potential effects on the environment before they can be allowed to proceed.
An EIA shall identify, describe and assess the direct and indirect effects of a project on the following factors:
The directives lay down rules for the EIA procedure, which includes a requirement for public participation: the results are to be made public, and the views of the public taken into consideration in the consenting procedure.
Wind energy projects are specifically mentioned in Annex 2 of the Directive 97/11/EC, indicating that the individual member states shall determine, either through a case-by-case examination or through thresholds or criterions set by the member state, whether wind power projects shall be made subject to an assessment.
In this way member states may exempt a specific project from the provisions in the directives, but it is unlikely that any offshore wind farm may be publicly approved without an EIA because of its size and the public attention regarding its environmental effects.
Developers of offshore wind farms must carry out an EIA on the specific project, with the purpose of providing information about the possible impacts on the environment from the time of installation till the dismantling of the turbines and foundation.
The EIAs from individual offshore wind energy projects will contain much valuable information regarding the effects from wind energy on the environment, but due to the fact that the experiences with offshore wind power are still relatively limited, the literature on environmental impacts appears sparse. In some cases the first pilot studies are only now underway. Currently only Denmark, Sweden and UK have put a few relatively small offshore farms into operation, and in Holland a semi-offshore farm is in operation.
The lack of experience with offshore farms and the impacts from here is clearly reflected in the responses to the questionnaires.
Only a few case studies on the impact on fish, birds, sea mammals and flora have been carried out in connection with the offshore plans already established, either as part of the Environmental Impact Assessments or as individual studies. Nevertheless, the response on the questionnaires clearly indicates that this knowledge has not yet been compiled in any systematic manner, resulting in the fact that the biological impacts and mechanisms involved are still being covered by uncertainty.
Biological issues considered potentially problematic were indicated as:
Collision of birds with turbines
Ousting birds off their traditional feeding/roosting grounds
Unknown effect of low frequency noise emissions on fish life and sea mammals
Impacts on fish larvae
Disturbances of seabed and fauna during construction and operation.
In the EU, different terms for bird-protected areas exist, the most important regarding offshore conditions being: Important Bird Areas (IBAs), Special Protected Areas (SPAs), Special Areas of Conservation (SACs) and Ramsar areas.
Only the term IBA will be used in this report, for the following reasons:
The answers to the questionnaires and the ranking of the subject show that the impacts on birds from offshore wind turbines are considered to be of very high importance in Europe in Holland, for instance, the impact on birds is the most important environmental factor according to the government, and when ranking the different issues in the questionnaire, the importance is also reflected in the fact that the impact on birds (and the visual impact) received the highest importance score of all environmental subjects from the members of the Concerted Action.
It is difficult to pose any general conclusions about the possible impacts for the following reasons:
the impacts are site dependent (e.g. distance to shore, presence of fish, migrations routes).
the impacts are relative to various bird species.
only a few studies have been carried
out for offshore wind turbines:
In Denmark, at Tun Knob offshore wind farm, Before-After-Control-Impact and After-Impact studies were conducted from 1994-97, but the results that no effect of the ten 500 kW wind turbines could be detected on the abundance and the distribution of Eider ducks were only valid for wintering Eiders [vi].
In Sweden, two studies on migrating birds at Utgrunden and Yttre Stengrund are being carried out, but with no definite conclusions available yet. 
the studies carried out for onshore wind farms in some cases present conclusions that contradict each other, some studies showing that birds avoid the vicinity of wind turbines (The Greenpeace Study [vii]), other studies concluding that onshore wind turbines have only little or no impact at all on bird life (e.g. [viii] and [ix]).
Impacts on birds may be expected, such as:
collisions of migrating or feeding birds with turbines (rotor)
turbines acting as barriers between feeding and roosting grounds or in migrations routes
ousting birds off their traditional feeding/roosting grounds due to physical changes of habitat