The City of Hamilton estimates 337 million litres of sewage — roughly 135 Olympic-sized swimming pools worth of sewage — flowed into the harbour since 1996. That's roughly 13 million litres per year for 26 years. "City staff developed this estimate based on the water meter usage data for all of the properties connected to the combined sewer pipe," read a media release from the city on Monday morning, adding this method was identified as the most accurate way to represent the discharge over the 26 years.