Was fighting a drowned trident and using a blunderbuss. I had a mod called particular which is a fabric version of effective. This did not have a problem before but somehow it turned into a ticking entity bug.

https://mclo.gs/HwXvzG7 = Log

https://mclo.gs/8aBkplU = Crash Report

Interesting - this even seems like it could affect Vanilla. I will fix this in about 7-10 days when I am finally home again.

The fix now relies on this: Chailotl/particular#41
On BWM: Legacy's side, no fix is needed, actually (and this was a pretty well known issue as indicated by the issue linked above).
The next version of Particular hopefully includes my fix :)

Thanks for reporting this!

Edit: Also, in the meantime, you can disable the water particles in Particular's config as a workaround. This will fix the issue for the time being (setting waterSplash).