The Thunder Bay District Health Unit samples from mid-June to the end of August. City beaches are sampled weekly (and posted with signage permanently), rural beaches are sampled three times per summer, and district beaches are sampled twice per summer. When the information is posted on the TBDHU website, Swim Drink Fish updates Swim Guide. As of 2018, Ontario beaches are following the Operational Approaches for Recreational Water Guideline, 2018, and the Recreational Water Protocol, 2018, for geometric mean and single-sample maximum parameters. These are now equivalent to those set out in the Guidelines for Canadian Recreational Water Quality – Third Edition, 2012: Geometric mean concentration (minimum of five samples): 200 E. coli/100 mL. Single-sample maximum concentration: 400 E. coli/100 mL. (These values replace the previous, more stringent Ontario standard: a geometric mean of 100 E. coli/100 mL.)

A beach is marked Green when the geometric mean of 5 samples collected within a 30-day period is below 200 E. coli / 100 ml of water and the single sample value is below 400 E.coli/100mL. A beach is marked Red when the geometric mean of 5 samples collected within a 30-day period exceeds 200 E. coli / 100 ml of water and/or exceeds the single sample value of 400 E.coli/100mL. A beach is marked Grey when reliable or up-to-date information is not available. DISCLAIMER: Historical data from 2017 and prior reflect the previous Ontario standard of a geometric mean of 100 E. coli /100 mL. Historical data from 2018 onward reflect the new Ontario Operational Approaches for Recreational Water Guideline, 2018: Geometric mean concentration 200 E. coli/ 100 mL and single-sample maximum concentration of 400 E. coli /100 mL.