Whale watchers aboard a tour boat off Victoria were treated to a rare sight Tuesday.

A military submarine was spotted traversing Canadian waters in the Strait of Juan de Fuca, just off the Race Rocks Ecological Reserve, southwest of the city.

A spokesperson for the Royal Canadian Navy's Maritime Forces Pacific confirms the submarine isn't one of ours, leaving only one likely culprit.

The Americans, however, aren't saying much, as per submarine mission protocol.

"Due to our operational security we are not making comment on any of that," U.S. Navy Lieut. Mack Jamieson told CTV News.

"We're being very selective with any kind of operational information we put out."

Jamieson is the spokesperson for the U.S. Navy's Submarine Group Nine, based out of Naval Base Kitsap in Bremerton, Wash.

The base, the third-largest in the U.S., is home to several Ohio-class ballistic missile and Seawolf-class fast-attack nuclear submarines.

Tour boat operator Paul Pudwell with Sooke Coastal Explorations captured video of the vessel as it cruised through the strait.

While he's seen submarines in the strait before, he said he's never gotten so close to one.

Canadian Navy Lt. Tony Wright said it's not unheard of for American warships, submarines and coast guard vessels to pass through the Canadian side of the strait, granted they check in with authorities and are monitored until they reach open water.

"I can confirm that this is not a Canadian submarine," Wright said.

UPDATE: On July 11, 2019, the U.S. Navy confirmed the vessel is an American submarine. "We can confirm that a U.S. submarine conducted a routine transit through the Strait of Juan de Fuca, parts of which are in Canadian territorial waters," U.S. Navy Cmdr. Nate Christensen told CTV News.