CHEMSEA was a cooperation of leading scientific institutes and maritime decision makers, established in order to assess and minimise risks related to sea-bottom activities near the known or suspected Baltic underwater dumping sites containing chemical warfare agents (CWA). CHEMSEA was dedicated to detection and mapping of the actual locations of CWA objects in the known dumping areas, and sediment pollution. The focus on marine organisms was limited mostly to Bornholm Deep with its specific conditions. CHEMSEA introduced the biomarker approach to observe biological effects of contamination on the health of organisms, including exposure experiments and insitu observations. Important output of CHEMSEA is the Center of Excellence for Dumped Munitions (CoEDCM) created as a hands-on transnational analytical center of CWA related hazards.