This study was carried out during the summer of 2007 in five lakes in the Åland Islands; the Lake Vargsundet, Lake Markusbölefjärden, Lake Långsjön, Lake Östra Kyrksundet and Lake Västra Kyrksundet. The aim of the study was to get information on fish and crayfish stocks in the lakes. Test fishing for crayfish was performed three times in each lake. Test fishing for fish was performed three times in the Lake Vargsundet and ones in the rest of the lakes. Seining for juvenile fish was performed twice in the Lake Vargsundet. All investigated lakes were to some extent eutrophicated and had large or very large fish stocks. The Lake Markusbölefjärden and Lake Långsjön, which are highly productive lakes, had very large fish and crayfish stocks. The crayfish stocks consisted mainly of large individuals (10–12 cm), which might indicate problems in recruitment. The Lake Östra Kyrksundet had a large crayfish stock that consisted mainly of small individuals, which might indicate intraspecific competition. The Lake Västra Kyrksundet had a normal crayfish stock and a slightly smaller fish stock than the other lakes. The Lake Vargsundet, which is a deep and meromictic lake, had a large fish stock but a small crayfish stock. Results of the seining indicate that there was recruitment of fish in the Lake Vargsundet. Annual monitoring of the crayfish stocks is recommended in all the investigated lakes. In the Lake Markusbölefjärden and Lake Långsjön we recommend a future study to verify if small crayfish exist in order to determine whether or not the crayfish populations in these lakes suffer from recruitment problems. In the Lake Östra Kyrksundet we recommend that the crayfish stock is followed up carefully in order to get verification on if the trend towards a larger stock with smaller individuals continues. Fishing for crayfish can proceed as before in the Lake Markusbölefjärden, Lake Långsjön, Lake Västra Kyrksundet and Lake Östra Kyrksundet. In the Lake Vargsundet a break in fishing for crayfish is recommended until the stock has recovered
