An unexploded hand grenade and a prehistoric beast were among the finds in a clean-up of the Thames foreshore in Fulham today.

Police specialists had to be called in to dispose of the grenade, which was discovered close to Fulham FC's Craven Cottage ground at around 10am by a group of volunteers working with the clean-up charity Thames21 .

A woolly mammoth caked in mud also generated excitement – but was quickly revealed to be a cuddly character from the animated movie Ice Age .

Around 100 people took advantage of the sunshine and the lowest tide for five years by making their way on to the foreshore at Bishops Park.

They collected around five tons of rubbish, along with other interesting finds such as a part of an old helmet and a 1970s-style roller skate, in the first half of a two-day operation to clear up the river in Hammersmith and Fulham.

Judith Ressler, river programmes coordinator for Thames21, said: "We found a shopping trolley, three bikes, three traffic cones and a hand grenade. We had to call the police and clear the area, because you never know if they're going to explode and we have to make sure everything is safe.

"We got a good amount of volunteers coming down and I'm very pleased with the way it's gone."

A police spokeswoman said the hand grenade was made safe at the scene.

A second day of activity is planned tomorrow to tackle plastic bags accumulating in the silt on the south side of Hammersmith Bridge. Volunteers are welcome to turn up between 11am and 1.30pm, and wellies will be provided.

For more information visit Thames21's website .