[en] To get information on the possible effects of future releases of radioactive effluents into Tvaeren, a bay of the Baltic, the Atomic Energy Company has had to carry out a biological and radiological programme in Tvaeren. The work was scheduled to extend over at least two years but in fact proceeded from 1957 to 1963. Unfortunately, no exact idea of the natural activity could be gained on account of the fallout from the repeated atomic bomb tests. Instead, the work developed into a study of the variations in biological samples caused by these tests. This report studies the correlation between the activity in fallout and that in flora and fauna. The contribution of natural activity from the radionuclide K-40 has been determined and is given for all samples. The following values may be regarded as representative of total β-activity and activity of K-40 in the investigated samples. T 1204 has been used as standard