Massive balloon releases might look pretty and be a good way of promoting a cause, but experts say they're bad for wildlife, and should be banned.
The number of balloons found on UK beaches has more than tripled in the last 12 years, according to the Marine Conservation Society (MCS).
Experts say they're bad because animals can swallow them, or get tangled up.
They say that animals like dolphins, whales, seabirds and turtles have already died.
Charity workers say they don't want to spoil anyone's fun, but are urging councils and event organisers to think of doing other things, instead of launching loads of balloons at once.
Birds like seagulls could be at risk
For example, a car dealer filled a car with balloons, instead of releasing them into the sky.
They also want balloons to be filled with air rather than helium gas, which makes them float up into the air and drift for miles into the sea.
Gill Bell from the Marine Conservation Society said: "A balloon release is not a cause for celebration, but a possible death sentence for an animal."