Paris Mayor Anne Hidalgo’s swim aimed to assure Olympic athletes, slated to compete there later, that the river was safe|Web Summit|CC BY 2.0

Paris Mayor Anne Hidalgo took a swim in the Seine River to demonstrate its cleanliness despite earlier concerns over high E. Coli levels.

The dip aimed to assure Olympic marathon swimmers and Olympic and Paralympic triathletes, slated to compete there later, that the river was safe.

Swimming in the Seine has been illegal for over 100 years due to high pollution levels, but after a $1.5 billion cleanup effort, the waters seem clean.

Last week, French Sports Minister Amelie Oudea-Castera also swam in the Seine.

While the Seine appears ready for the triathlons, organizers lack an alternate location should heavy rain jeopardize water quality or the flow.