Thermophilic Campylobacter species have been implicated in human gastrointestinal infections and can occur in agricultural run off, sewage discharges, and the feces of domestic and wild animals including birds. A 2-year study was designed to investigate the occurrence of the primary thermophilic Campylobacter species (C. jejuni, coli, and lari) associated with human disease at 5 recreational beaches on Lake Simcoe, Ontario, Canada. A biweekly sampling program involved collecting water samples across 3 depth zones (sand pore water and ankle- and chest-depth waters). To identify the potential sources of contamination, samples were also collected from 4 neighboring rivers corresponding to selected beaches, a few fresh seagull and Canada geese fecal droppings on beaches, and a stormwater outfall. Water and fecal samples were processed for Campylobacter spp. isolation and detection using a minimum probable number culture enrichment protocol. Thermophilic Campylobacter spp. generally occurred infrequently and at low concentrations (≤30 cells L-1) at all sampling locations; they were detected in 12% of water samples from beaches (n = 289) compared to 14% from rivers (n = 100). C. jejuni and C. lari were the species most commonly detected. Nine isolates identified as unknown Campylobacter spp. were further sequenced and shown to be more closely related to Arcobacter spp. At beaches, thermophilic Campylobacter spp. were generally detected more often in sand pore water than in ankle- or chest-depth water. The study suggests that sand, rivers, and bird droppings could be potential sources of Campylobacter spp. contamination at Lake Simcoe recreational beaches. 
