In Sweden there are about 140 different species of fish, of which the Royal National City Park has around 40. Many of the watercourses are eutrophied, which has caused them to clog up. Trees and bushes which shade the water can be planted in order to reduce this overgrowth and protect the fish, but the most important action is to stop further pollution and eutrophication of the water.
The introduction of new species of fish, especially in previously fish-free water, can have far-reaching consequences for the natural environment. The introduction of carp has had detrimental effects on bird life in the smaller watercourses such as Isbladskärret and Lappskärret. For sport fishing, Stockholms Ström is a good place to fish and amateur anglers are often to be seen at Norrbro and elsewhere.
The photo shows a stone loach, Barbatula barbatula, one of Sweden’s less common species of fish which can be found in the Royal National City Park. One of its few haunts in Svealand is Igelbäcken, which runs through Uriksdal. The stone loach is a small fish that is nocturnal and seeks shelter under stones and roots in slow-moving waters. It is believed to have come to Sweden from Germany in the 18th century when king Fredrik I introduced the relatively similar weather loach (Misgurnus fossilis). Some stone loach may have been included and have survived, whereas the weather loach no longer exists in Swedish waters.
So far the conservation measures which have been undertaken in Igelbäcken by adding sand and gravel have had a positive effect on the stone loach, which can now be found throughout Igelbäcken from its estuary in Edsviken up to the Järfälla municipal border.