Seas around the UK are in crisis according to the WWF, with numbers of some important species dropping.
The Marine Health Check Report looked at 16 creatures and the places they live and found 13 of them dying out.
The WWF says too many things like fishing and looking for oil and gas are taking place in our seas without enough planning before they happen.
Five years ago the WWF warned that some of these problems could happen, and say now those threats have become reality.
Taking gravel and sand from seabeds is another problem, and is changing the places where many sea species like to live.
The WWF wants the sea to be treated the same way as dry land, where much more consideration to the environment is given before any changes are made.
The charity's Senior Marine Policy Officer, Jan Brown, said scientists were now discovering plants in the sea that could become medicine, but added they could destroyed before we get the chance to use them.