The Neolithic site Rinnukalns in the Lake Burtnieks/River Salaca area in northern Latvia is the only freshwater shell midden in the eastern Baltic Sea area. An excavation carried out in 2011 revealed an intact stratigraphy with alternating layers of unburnt and burnt mussel shells and yielded various kinds of archaeological finds, among them several thousand fish remains. To get an impression of the fish species and specimens caught by the Neolithic settlers, and to look for a temporal development in the fish species composition, we analysed fish remains from different sections and layers. The results, both archaeozoological and stable isotope data, give evidence for a change in the relevance of fish species during the period of use, and they also provide an impression of the former river and lake hydrology in the vicinity of the midden. The Stone Age landscape seems to have been very similar to the present situation, so that the study area has been an extraordinarily stable ecosystem for more than 5000 years. Comparisons with the results of recent monitoring programmes, with long-term changes since Medieval times, as well as with written sources from the 18th century, show that the fish species community is almost unchanged since the Stone Age. This underlines the importance of the region in nature conservation.