KANALERNA I GÖTEBORG – VATTEN OCH FISKAR – EN MILJÖBIOLOGISK STUDIE / The Canals in Göteborg – Water and Fish – an Environmental Biology Study

Investigations and studies of documentation show that the situation for the fish and the water quality in the Göteborg canals are better than 100 years ago thanks to the early construction and successive improvements of the sewer system. The river Göta älv has nowadays the greatest influence of the water quality in the canals due to the tidal water variations influence on the water exchange in the canals. The analysis results of of the water samples taken from the canals show great variations and some samples of the water fulfil the bathing water criteria. There have been many occasions when the microbiological water analysis clearly indicated that the canals normally is not appropriate for bathing. If the water quality in the channels can improve further depends mainly on if the water quality in Göta älv can be improved. The result of analyses of sediment samples, water samples and caught fishs show that the canals are slightly influenced by heavy metals (copper, zinc, and earlier also lead) mainly from storm water and previous waste water outlets. Heavy metals in the sediments can pollute the water if the sediment are mixed with the water. The heavy metals in the sediment probably make less harm if they remain in the sediment. Dredging and boat traffic should be avoided as it can mix the polluted sediment with the water. Long time studies (1974–2003) and comparisons with previously documented species of fish show that the number of fish species has changed through the years of human influence. Earlier, the number of fish species has decreased, but in the latest 20 years the fish species has increased. Accumulation of different substances in the fish reflects the background load on the water environment. Fish caught at the yearly canal fishing competition are today eatable without any restrictions according to present norms. A continuous decrease of heavy metals in the fish has been observed during the period studied. The high oxygen content in the water seems, in long time perspective, a more important factor for the development of the number of fish species. In the beginning of 1970-ties, 10 different fish species were known in the canals. Recently, 22 different fish species have been observed. The study shows clear connections between improvements in the sewer systems, improvements of water quality in the canals, number of fish species in the channels and reduced levels of pollutants in fish.