Eutrophication of lakes, rivers and coastal waters is the main environ
mental problem caused by agriculture in Finland. Water quality of most
Finnish watercourses is good or excellent, but in the intensively cul
tivated region of southern and western Finland the turbidity of water
as well as algal blooms are a common problem. Generally, phosphorus is
the limiting nutrient for primary production in Finnish lakes, but in
eutrophic lakes and coastal waters the role of nitrogen becomes more
important. Nitrogen from agriculture enters the watercourses mainly in
dissolved form. By contrast, most phosphorus is transported in associ
ation with small particles. According to bioassays the algal availabil
ity of this particulate P is very low. Therefore, the eutrophying effe
ct of agriculture can be estimated on the basis of dissolved nutrients
. In shallow lakes, typical in agricultural regions, the release of di
ssolved P from the bottom sediment often induces the development of N2
-fixing blue- green algal blooms. In some cases the internal load may
exceed the external load. For the recovery of such a lake the introduc
tion of better agricultural practices in the drainage basin has to be
coupled with in-lake measures.