Two men who claim they have been exploring and photographing Toronto's network of sewers for six years appear to have explored one too many Sunday night and are facing charges of mischief as a result.

Michael Cook and Andrew Emond, geared up with head lamps and hip waders, entered the sewer system near Ossington Avenue and Dundas Street West, police said.

A passerby spotted them climbing into the sewer and called police, who showed up with four fire trucks and a hazardous materials team.

Four hours later, Cook and Emond were found, arrested and charged.

Toronto police Det. Dan Hoffmeyer said storm sewers can be dangerous.

"Down there, there's poisonous gasses," he said. "Hazmat crews here go down with breathing apparatus, or they just [send] down [a] video camera — they don't go down personally.

"There's [also] a chance of the tunnel filling up in a matter of minutes and people drowning. If there was a storm somewhere, they'd fill up in a matter of seconds."

According to a website run by Cook and Emond, www.vanishingpoint.ca, they've been exploring and photographing the underbelly of Toronto for six years and recording the finds on the site.

There's no word yet on what Sunday night's search and arrest cost the city.

When asked about the legality of entering the sewer system, Hoffmeyer said: "I guess without permission [of the city], yes, it's illegal."

Whether all of the men's previous forays into Toronto's underground were without permission, he said he had no way to know.