This might look like a carpet or woolly blanket, but it's really thick green algae that's causing big problems in China.
The blue-green weeds are smothering the water in the coastal town of Qingdao - one of the main sailing venues for the Olympic Games.
They're causing problems for sailors as they are very strong and stringy, making it really tough for boats to sail through.
A massive clean-up is under way to try to get rid of the algae, which is said to feel like wet wool or hair and smell like overcooked spinach. Yuck!
The weeds started to invade the coastline at the end of May and have steadily spread to cover most of the water and beaches around the Olympic course.
More than 1,000 boats and 10,000 volunteers are involved in the clean-up.
This swimmer looks like he's made himself a shawl out of the weeds. Doesn't look too warm though does it?
So far, 100,000 tonnes of the weeds have already been removed but officials think it could take another two weeks to get rid of them completely.