RCMP in B.C. say they think they know who caused a major diesel spill on a remote West Coast island, but in this case, it seems unlikely the Mounties will get their man.

Diesel fuel was spotted recently seeping into the water and onto the banks near the fishing village of Bella Bella on Denny Island.

The boat-access-only village is located in B.C.'s Inside Passage about halfway between the northern tip of Vancouver Island and the port town of Prince Rupert.

Over the weekend the source of the fuel spill was traced to a tank perched about 100 metres up a hill behind a fishing lodge.

The tank's valve was found open and an estimated 4,000 litres had drained out, according to Const. Aaron Muzzerall of the Bella Bella RCMP.

At first police and locals suspected it was vandals who left it open.

But police soon deduced it was a saboteur of a different species after closely examining the marks on a small plastic bag secured over the valve, said Muzzerall.

"There are signs of a very large bear being in the area and it had gone up and left teeth marks and bite marks in the Ziploc bag and inadvertently pulled the valve open, and this is how the leak started," he told CBC News on Monday.

Police now believe the bear was either attracted to the diesel fuel or something in the plastic bag.

And while the circumstances are amusing, Muzzerall said the damage is not.

The slick from the diesel now stretches for about five kilometres from the site, and a layer of fuel is clearly visible on the shoreline. It is not clear how long the cleanup will take.