(ERROL MCGIHON/QMI AGENCY)

OTTAWA — Heavy rain has caused more than 15 million litres of sewage to spill into the Ottawa River.

The city of Ottawa reports 15.3 million litres of sewage went into the water body because the combined sewers overflowed.

Combined sewers hold both storm water and sewage. When there's a lot of rain in a short period of time, the sewers fill beyond capacity and the guck runs into the river.

It is the third combined sewer overflow in Ottawa due to rainfall this year.

The city says the combined sewer overflows don't affect drinking water.

The city is currently celebrating "drinking water week."