# Deep Water *Environmental Hazard* Swimming through deep water (more than 100 feet deep) presents additional challenges because of the water's pressure and cold temperature. After each hour of swimming in deep water, a creature that lacks a Swim Speed must succeed on a DC 10 Constitution saving throw or gain 1 [Exhaustion](Mechanics/CLI/rules/conditions.md#Exhaustion) level. *Source: Dungeon Master's Guide (2024) p. 68*