There are a few ways a species can be removed from the endangered species list. Scientists can discover different information that changes their assessment of the species. Or, policies enacted to protect the species could work, and population numbers rise to the point the species is no longer considered endangered. That is the best-case scenario.

A species can also be removed because they are extinct in the wild. That is the worst-case scenario.

In a new proposal from the U.S. Fish and Wildlife service, 23 species are now facing that worst-case scenario. The proposal recommends taking almost two dozen species off of the endangered and threatened species list. The fact is a species cannot be endangered if it no longer exists on the planet.

The list consists of multiple birds, including the bridled white-eye and the ivory-billed woodpecker, and a number of freshwater bivalves. According to the International Union for Conservation of Nature, freshwater species are going extinct at a higher rate than terrestrial or marine species, with one third of all freshwater species facing extinction. They’re primarily threatened by habitat loss, invasive species, climate change and more.

Here are a few of the aquatic species mentioned in the proposal:

• Green blossom (pearly mussel) (Epioblasma torulosa gubernaculum): This freshwater mussel was originally listed as endangered in 1976 and was threatened largely due to habitat destruction. Originally found in tributaries of the Tennessee River, the green blossom has not be seen since 1982.
• San Marcos Gambusia (Gambusia georgei): This small freshwater fish was found in the San Marcos River in Texas and greatly affected by pollution, habitat degradation and increasing drought. No individuals have been seen in the wild since 1983, and despite captive breeding efforts, none have survived in captivity since the mid-1980s.
• Scioto madtom (Noturus trautmani): A small catfish found in Ohio, only 18 were ever collected from the wild. Although scientists aren’t certain of the cause of its population decline, they suspect it was because of habitat disruption, agricultural runoff and, potentially, competition with another species of madtom. No Scioto madtoms have been seen since 1957.

Although no marine species were included on the proposal, the list indicates ongoing threats to all species. These are only species that we have research to support their discovery and subsequent loss—it’s especially harrowing to think of all the plants and animals that might be approaching extinction without our knowledge!