Per- and polyfluorinated alkyl substances (PFAS) are a group of organic chemicals that, due to their strong molecular bonds, are highly persistent. Because of this, PFAS are today a global pollutant that contaminates our crops, soils, and drinking water reservoirs. This study focuses on analysing PFAS in Lake Bolmen (southwest Småland, Sweden). Drinking water production is extracted in the southern part of Lake Bolmen, thus this study examines if PFAS concentrations exceed recommended Swedish limit values for safe drinking water for PFAS4 (4 ng/l) and PFAS21 (100 ng/l) in Lake Bolmen’s raw water, with particular focus on the southern parts. In addition, the study examined the impact of a point source, an abandoned military airfield, on PFAS concentrations in Lake Bolmen, and the connection of these legacy PFAS to firefighting foam type B, commonly used in military exercises. The concentration of different types of PFAS was studied during two different time periods: from October 2023 to August 2024, and from January to March 2025 at twelve locations in and around Lake Bolmen. The results showed PFAS concentrations in lake water in the southern part of Bolmen, specifically at the sample site closest to the abandoned airfield. Here the drinking water limit for PFAS4 was exceeded in multiple locations while PFAS21 only exceeded the limit at one site. At the sites with high PFAS concentration, the majority of PFAS compounds could be connected to firefighting foam B. Further continuous monitoring of the PFAS concentration in Lake Bolmen is essential for ensuring safe drinking water production. Additionally, the study shows that monitoring of, and research on, ultrashort chain PFAS is of importance, since there is a clear knowledge gap concerning ultrashort PFAS environmental concentrations and proliferation.