Millions of gallons of wastewater, including raw sewage, are either dumped or spilled from local treatment plants across the United States each year, especially during hurricanes and floods.

The sewage goes into lakes, rivers, bays and ditches. Some of it ends up flowing down streets, or through fields and parks.

It can carry bacteria and parasites, as well as remnants of all sorts of things excreted by the human digestive tract, including evidence of opioids, polio and, now, coronavirus.

(WATCH: Can Coronavirus Spread in Pools and Hot Tubs?)

In recent weeks, cities and counties across the nation have begun to monitor the markers of coronavirus in their wastewater, in the hopes of getting a more accurate look at how many people might have contracted COVID-19 and to help predict future waves or peaks of infection.

But could all those gallons of leaked and spilled wastewater also spread the disease? So far, there's no evidence any signs of coronavirus in sewer water could infect anyone who might come into contact with it, experts say.

"These are virus particles that are mostly intact but that are no longer infective," Krista Wigginton, a professor of environmental engineering at the University of Michigan who is working on a project to track coronavirus in wastewater, told NPR.

The World Health Organization says there is no evidence of coronavirus being transmitted from either treated or untreated wastewater.

The U.S. Centers for Disease Control and Prevention says this on its website: "The virus that causes COVID-19 has been found in untreated wastewater. Researchers do not know whether this virus can cause disease if a person is exposed to untreated wastewater or sewerage systems. There is no evidence to date that this has occurred. At this time, the risk of transmission of the virus that causes COVID-19 through properly designed and maintained sewerage systems is thought to be low."

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Sewer spills can happen at any time, but are especially prevalent in coastal areas during flooding or hurricanes, when systems might become inundated, pipes break or power outages force backups.

Hurricane Sandy in 2012 caused more than 10.9 billion gallons of sewer overflow in nine states, according to a report by Climate Central.

Flooding after the short-lived Hurricane Barry last summer caused more than 250,000 gallons of sewage to be dumped into waterways along Alabama's coastline.

Communities in Florida are among the worst offenders. An investigation last year by GateHouse Media showed that some 1.6 billion gallons of wastewater was leaked or dumped from sewer plants across the state in the past decade, including 370 million gallons of raw, untreated sewage. Some of it came during hurricanes and storms, but many spills happened simply because sewer systems are outdated and overwhelmed.

Florida's spills in particular have been blamed for closing beaches, fueling toxic blue-green algae blooms and possibly feeding large outbreaks of red tide in recent years.

Some of the communities that are monitoring their wastewater for coronavirus as a tool to fight the pandemic are the same ones that have had large sewer spills in the past, and are at risk for them again.

For the latest coronavirus information in your county and a full list of important resources to help you make the smartest decisions regarding the disease, check out our dedicated COVID-19 page.