Polar bears and hippos have joined a list for the first time of species close to being wiped out.
They've been included on the Red List of Threatened Species put out by the World Conservation Union (IUCN), which names more than 16,000 at-risk species.
Lots of fish and sharks have also been put on the list for the first time.
The IUCN say numbers of species are still falling despite an agreement which committed governments around the world to fight the problem.
Achim Steiner, head of the IUCN, said the falling number of species could have a big effect on billions of people who depend on them.
It's thought polar bears have been badly affected by climate change.
They need lots of ice to hunt on and to raise their cubs. As more ice melts because of rising temperatures, they are finding it hard to survive.
Numbers of the common hippopotamus in the Democratic Republic of Congo have fallen by 95% in the last 10 years.
That's because unrest in the country has allowed poachers to hunt them for ivory in their teeth.