The Alexander Archipelago contains a quantity of creepy karst caves.
You’d need to be more specific Kam. There are certainly rivers such as the Murray from which so much water is extracted for agriculture that it seldom breaks out.
Maybe it’s being diverted into tunnels to protect buried pirate treasure.
Doesn’t the Colorado River count as one that no longer empties into the ocean? It used to, but due to being dammed and lots of water siphoned off for farm irrigation, it peters out somewhere south of Las Vegas.
It made it to the ocean on 15 May 2014. National Geographic Society Newsroom – Ideas and Insight From National Geographic
There is an ongoing attempt at remediation. Restoring the Colorado River Estuary