Cleaning up after thousands of beavers formed part of the latest Serious Ocean challenge for a group of intrepid child adventurers.
Thirteen-year-old Harry was one of a group of teenagers who travelled to Tierra del Fuego in South America for the hit CBBC show.
Tierra del Fuego is an almost uninhabited area of natural beauty that's being destroyed by beavers.
Beavers chew through the tree trunks
To get there, Harry and the others had to pass glaciers and trek through an ancient forest.
"I sat in a dam that the beavers built and it was absolutely amazing to see that such small creatures had built such a big structure," he said.
"Unfortunately, to create their homes the beavers have completely destroyed the area by blocking rivers and cutting down trees with their razor-sharp teeth."
Out of control
Beavers never used to live in the area until the 1940s, when 50 of the critters were introduced from Canada to breed for their furry coats.
But the animals multiplied out of control and now there are up to 100,000 of them.
Because of the damage they are causing to the natural plants and wildlife, scientists want to cull the beavers to protect the area.
Conservation expert Chris Anderson said: "In conservation, sometimes we have to do things besides just protecting species.
"When we have harmful species, like invasive species, we also have to control them.
"So it's important to realise that as people, we're responsible for taking care of this problem we created."
During their mission, Harry made a grim discovery when he found a beaver in one of the traps.
Removing one of the beavers' dams
"To find a beaver dead in a trap is quite horrible really," he said. "Although the traps are humane, killing the beavers instantly, I wasn't the only one upset by the trapping."
His Serious Ocean team-mate Robyn agreed, saying: "I know we have to kill them and I know it's a good thing that we found one and everything, but seeing it is really sad."
Before leaving the area, Harry and his mates also helped remove some of the beavers' dams to allow the river to flow again and help restore the area to its natural beauty.
You can watch Serious Ocean on CBBC from Wednesday 9 July 2008.