Heavy rain swamped Tampa's sewage collection network Monday evening, spilling about 329,000 gallons of untreated wastewater into the Hillsborough River.

Across Tampa Bay, St. Petersburg had its own, much smaller spill on the eve of a mayor's race in which the city's wastewater problems have been a central issue.

In Tampa, the bigger of two spills took place just north of the Columbus Drive bridge from an emergency overflow pipe on N Perry Avenue. There, 290,000 gallons spilled into the river from 6:45 to 11:05 p.m.

It's the same spot where 352,000 gallons spilled into the river during heavy rain dumped by Tropical Storm Colin in June 2016. (In August 2015, heavy rains likewise overwhelmed the system, popping manhole covers out of place around the city as rain surged through sewers.)

"Obviously, it's a direct result from the rain," Tampa Wastewater director Eric Weiss said Tuesday. The spill took place just upstream from a low spot where a wastewater line goes under the Hillsborough River. If the system is going to back up, officials would expect it to do so at such a low spot.

Still, Tampa officials are looking at the operation of the city's 230 pumps during the storm to determine whether they could have been operated differently to prevent the spill. In the past, the city has looked into coordinating the use of pumping stations upstream to slow the flow of wastewater and take advantage of spots in the system where some water can be held so that the flow into the treatment plant is more even.

Weiss said the city's Howard F. Curren Advanced Wastewater Treatment Plant was able to handle and treat all the sewage that reached the facility without any problems. For several hours Monday night, the plant was taking in water at a rate of 170 million gallons every 24 hours.

"It's a lot of rainfall in a very short period of time," Weiss said. The plant is permitted to handle 96 million gallons a day, but it has the capacity to handle surges flowing at as much as 200 million gallons a day.

He said the smaller Tampa spill, about 39,000 gallons, took place at W Minnehaha Street and the river, a few blocks south of Lowry Park, at the same time as the larger spill.

The city reported both spills to the Florida Department of Environmental Protection and will test water in the river in coming days for elevated levels of fecal coliform.

In St. Petersburg, 1,000 gallons were spilled when operators at the Southwest wastewater treatment plant started to implement a "bypass" to divert heavy flows into plant's headworks (the place where sewage initially flows into the plant). The spill took place between 8 and 8:30 p.m. Monday and was confined to the plant.

There was no risk to public safety, according to Public Works spokesman Bill Logan.

One of the big issues in St. Petersburg's mayoral primary between incumbent Mayor Rick Kriseman and former Mayor Rick Baker is how the Kriseman administration has handled the situation arising from the release of tens of millions of gallons of sewage from 2015-16.