The water quality of Linnéasjön, Nybro, have, at times, been poor for the last 35 years, and sometimes considerably so. Reported measurements of fecal indicator bacteria, such as Escherichia coli and enterococci, have repeatedly exceeded the general water quality limit and thus prohibiting swimming and recreational activities in the area. In this report, the aim was to track the fecal source or sources of the poor water quality. In total, more than one hundred environmental waters, raw sewage inlet waters, fecal samples from dog and wild bird were collected and sequenced. Moreover, to enhance the source tracking analyses, a dilution experiment was conducted where the fecal sources were diluted in the environmental water. Results of the source tracking and fecal indicator analyses suggested that both wild bird and sewage reduces the water quality as those sources were detected in most collected environmental water samples. In addition, fecal signals from dogs were weak and were not expected to have any impact on the water quality. The results of the analyses of the dilution experiment strengthen these conclusions.