Dolphins and squids seem to beach themselves very easily because of their movement while really close to shore. This leads to dolphins often short hopping onto land and squids dying randomly. Fish and guardians seem unaffected by this.
Note that the water depth doesn't seem to matter, just being close to land.
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violine1101
I've been seeing this too. Spent a few hours building near a river, and lost count of how many squids got washed up on the shore. Had over a stack of ink sacs dropped by beached squids in only a couple of hours.
Orbic
The squid issue is MC-132473.