The people responsible for safely diverting billions of gallons of stormwater from several Ramsey County communities have just released a video showing the critical role played by the “rivers” beneath our feet.

Thanks to a months-long repair project to a century-old system of storm sewer tunnels, called the Trout Brook Sewer System, officials with the Capitol Region Watershed District were able to shed light on not only the sewers themselves, but residents’ impact on what flows from their yards into the Mississippi River.

“When we started this project, we saw a large section lit up and we thought: ‘Wow, this is a perfect opportunity to take some nice photographs and video of the tunnel and show the community what happens beneath the ground,’ ” said Anna Eleria, division manager with the watershed district. “A lot of our work happens underground or in structures that are not evident to the general public. This was a chance to show the importance.”

The video offers a glimpse into a 6-mile underground tunnel system that travels from Como Lake in St. Paul and Lake McCarrons in Roseville and eventually carries stormwater to the Mississippi River. It carries 3.9 billion gallons of rainwater and snow melt from neighborhoods in St. Paul, Roseville, Falcon Heights and Maplewood to the Mississippi River.

Made of large limestone blocks, officials said the system is historically significant.

But it had missing or damaged mortar between those blocks in several places along its 6 miles. In addition to repairing mortar, crews have been installing a concrete liner in some places and removing calcium deposits. While much of the $1 million project has gone unnoticed, Jessica Bromelkamp, spokeswoman for the watershed district, said the system is important for public safety because it carries away runoff and alleviates the potential for flooding.

The tunnels were once used to carry sewage and stormwater. But Trout Brook has been a storm sewer system exclusively since the 1990s. None of the water is treated before it reaches the Mississippi. That makes the watershed district’s work with residents to keep their communities clean critical to the river’s quality, Bromelkamp said.

In 2015, the district started a pilot project with Hamline University and the city of St. Paul to encourage residents to adopt storm drains to keep communities, lakes and rivers clean. Residents are asked to keep leaves and other debris away from drains and report how much material they collect during the year.

In all, the Trout Brook system collects water from an 8,000-acre drainage area. Repairs, which began in December, are just now wrapping up, Eleria said. During the repairs, stormwater was diverted into a parallel storm sewer system run by the City of St. Paul.

The video of the tunnels is the public’s only chance to see the subterranean system, Bromelkamp said. Because workers need specialized training and equipment to safely enter the tunnels, they are not open to the public. The 4-minute video of the Trout Brook system can be seen online at vimeo.com/208134713.