While you're swimming, each foot of movement costs 1 extra foot (2 extra feet in difficult terrain). You ignore this extra cost if you have a Swim Speed and use it to swim. At the DM's option, moving any distance in rough water might require a successful DC 15 Strength (Athletics) check.
{
"name": "Swimming",
"page": 376,
"srd52": true,
"__prop": "variantrule",
"source": "XPHB",
"entries": [
"While you're swimming, each foot of movement costs 1 extra foot (2 extra feet in {@variantrule Difficult Terrain|XPHB|difficult terrain}). You ignore this extra cost if you have a {@variantrule Swim Speed|XPHB} and use it to swim. At the DM's option, moving any distance in rough water might require a successful {@dc 15} Strength ({@skill Athletics|XPHB}) check."
],
"ruleType": "C",
"basicRules2024": true
}