The way darkvision works underwater is unspecified, which probably means it works the way it does above water -- it negates obscurement due to darkness but not other causes.
Visibility underwater depends on water clarity and the available light. Use the Underwater Encounter Distance table to determine the distance at which characters underwater become aware of a possible encounter.
I'll assume it's about the same in clear water but reduced in murky water. Is there anything else about this ability I should know? Thank you.
Also, when throwing an unconventional object as a weapon (ie. plate, rock), how do I calculate range and damage? Thanks again.
The way darkvision works underwater is unspecified, which probably means it works the way it does above water -- it negates obscurement due to darkness but not other causes.
Unconventional objects use the rules for improvised weapons.
The biggest thing to remember IMO, which I frequently forget, is that in darkness, Darkvision gives vision as if in dim light.
If you dig deep enough you’ll eventually find this:
Underwater Visibility (https://www.dndbeyond.com/sources/dmg/adventure-environments#UnderwaterVisibility)
Visibility underwater depends on water clarity and the available light. Use the Underwater Encounter Distance table to determine the distance at which characters underwater become aware of a possible encounter.
Underwater Encounter Distance
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Darkvision does nothing against murk. The only thing I know of that counters murky water or murky air (fog/smoke) is blindsight.
A dolphin would totally ignore the murky water and ''see" as if it were clear, at least within 60 ft.
Thanks for replies. Seems like common sense.