The hot weather can make a river or canal seem like a great place to cool off.
But there is usually more in there than just fish - things that can be very dangerous for people who go swimming
A national survey looking at what objects lie beneath the surface of the UK's canals has uncovered some surprising items.
Rubbish thrown into rivers and canals cause big problems for wildlife and boats.
A four-month long survey found that an average canal lock - about the size of a tennis court - will contain:
The Canal and River Trust charity say that it costs them about £1 million each year to clear out what they can.
The bits that get left behind can trap wildlife, or poison the water, please keep safe stay away from canals and rivers.