How does an armadillo cross a river?

Armadillos don't float naturally, so they cross small bodies of water by walking across the bottom, like divers wearing weights. When they must swim, they can make themselves buoyant by gulping air to partially inflate their intestines.

http://www.bdb.co.za/shackle/articles/cane_toads.htm

Also, the nine-banded armadillo is the only armadillo species that can swim.

http://wonderclub.com/Wildlife/mammals/armadillo.html

They wade through bodies of water in one of two ways: walking on the bottom or with only their heads exposed and with their snouts above water.

http://www.tpwd.state.tx.us/publications/nonpwdpubs/introducing_mammals/armadillos/

They are good swimmers, although have trouble floating. Since they can hold their breath for up to 6 minutes this is not a big problem. As mentioned above, if it's a relatively small crossing they can just run along the bottom of the waterway and up the other side!

Armadillos like to swim, and they are very good at it. They have a strong dog paddle, and can even go quite a distance underwater, walking along the bottom of streams and ponds. They can hold their breath for four to six minutes at a time. When they need to cross larger bodies of water, they swim across. Because their heavy shell makes it hard for them to float, they gulp air into their intestines to make them more buoyant. The ability to cross streams and rivers has helped armadillos expand their home range. For more on this increase in armadillo range, see the Armadillo Expansion page.

https://armadillo-online.org/facts.html