Cyanobacterial harmful algal blooms (HABs) are becoming more prevalent, whether by human alterations or increased study across the USA and globally. Lake Fayetteville in northwest Arkansas has a long history of being dominated by cyanobacteria during summers, and in summer 2019 total microcystins were first measured and exceeded EPA’s recreational guidelines. Since then, this small (~0.6 km2) recreational lake has been the focus of various studies on HABs, including sediment P dynamics, nutrient limitation bioassays, and statistical modeling. In summer and fall 2024, we investigated the occurrence and effect of PFAS on HABs and microcystin concentrations on two sampling dates. The specific objectives were to sample the lake for 40 different PFAS compounds and evaluate the effect of one PFAS compound (PFBA) and one breakdown product (TFA) on microcystin concentrations in bioassays with lake water. We sampled the lake at three locations and its main inflow for PFAS, and lake water from near the dam at our routine sampling site was used in bioassays. Lake water was analyzed for PFAs using EPA Method 1633, and the lake water in the bioassays was spiked with nutrients and PFBA or TFA (both, 1 and 100 ug/L). We found several PFAS compounds in the inflow and lake water, including PFBA (~0.004 ug/L), PFPeA, PFHxA, PFHpA, PFOA, PFNA, PFDA, PFUnA, PFDoA, PFTrDA, PFBS, PFHpS, and PFOS. The number of PFAS observed increased towards the dam, showing both increases in the lake relative to the inflow and dilution. The addition of nutrients stimulated cyanobacterial growth (chl-a concentrations, chl raw fluorescence units (RFU), and phycocyanin RFU), increased total microcystin concentrations, but decreased total microcystin production. The addition of PFBA and TFA did not influence cyanobacterial growth nor total microcystin concentrations in the control (lake water) or nutrient treatments. Thus, several PFAS were observed in Lake Fayetteville, but PFBA and TFA did not influence microcystin.