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 level.
When the temperature is 0 degrees Fahrenheit or lower, a creature exposed to the extreme cold must succeed on a DC 10 Constitution saving throw at the end of each hour or gain 1 Exhaustion level. Creatures that have Resistance or Immunity to Cold damage automatically succeed on the save.
When the temperature is 100 degrees Fahrenheit or higher, a creature exposed to the extreme heat and without access to drinkable water must succeed on a Constitution saving throw at the end of each hour or gain 1 Exhaustion level. The DC is 5 for the first hour and increases by 1 for each additional hour. Creatures wearing Medium or Heavy armor have Disadvantage on the save. Creatures that have Resistance or Immunity to Fire damage automatically succeed on the save.
A creature can be immersed in frigid water for a number of minutes equal to its Constitution score before suffering any ill effects. Each additional minute spent in frigid water requires the creature to succeed on a DC 10 Constitution saving throw or gain 1 Exhaustion level. Creatures with Resistance or Immunity to Cold damage automatically succeed on the save, as do creatures that are naturally adapted to living in ice-cold water.
Traveling at altitudes of 10,000 feet or higher above sea level is taxing for most creatures because of the reduced amount of oxygen in the air. Each hour such a creature spends traveling at high altitude counts as 2 hours for the purpose of determining how long that creature can travel (see “Travel Pace”).
Creatures can become acclimated to a high altitude by spending 30 days or more at this elevation. Creatures can’t become acclimated to elevations above 20,000 feet unless they are native to such environments.
Slippery ice is Difficult Terrain. A creature that moves onto slippery ice for the first time on a turn or starts its turn there must succeed on a DC 10 Dexterity saving throw or have the Prone condition.
Strong wind imposes Disadvantage on ranged attack rolls with weapons. It also extinguishes open flames and disperses fog. A flying creature in a strong wind must land at the end of its turn or fall.
A strong wind in a desert can create a sandstorm that imposes Disadvantage on Wisdom (Perception) checks.