The Republic Aquatic Center was closed after the lawn mower was found early Sunday. The center is expected to reopen Tuesday morning.
The Springfield News-Leader reports crews cleaned the pool by midday Sunday, but the chemically treated water needed 24 hours before it could re-open to patrons.
The vandalism cost the city about $1,000 to treat the water and $6,200 in lost revenue.
A city of Republic news release said the vandalism was unfortunate for people who had events scheduled or classes at the center and for employees who lost hours and wages.