Whether or not it can be fixed is ultimately unknown, but you can try. Here is the link to the device page:

LINK

You can use the guides to take the DS apart to 1: get it dried out 2: check for and repair any damage caused by the water.

There will likely be oxidation on connections, and basically anything metal inside. You will want to clean this with >90% isopropyl alcohol and cotton swabs. The oxidation will usually be a white or green powder. Blow off what you can with canned air, then swab the rest. Be sure to use at least 90% alcohol, any lower percentage is diluted with water, and that would defeat the purpose.

Good luck!