Would Swimming be a Dex or Str Saving Throw?

Question

I'm making a small challenge for my party on the way to a Dwarven camp. While travelling they encounter a 20ft wide river that they must cross. I'm just gonna improvise the whole thing to give them some creativity in how to solve this problem.

My question is what happens if they fall in? The river has a strong current as it leads to a section of white-water rapids that is also being fed by an adjacent river making the current more deadly.

If they fall in I am giving the chance to make a Saving throw to try and swim across. What would make more sense: a dexterity or strength saving throw, or even maybe a check instead like athletics.

Also what DC for this check would you recommend for an 8th level party?

Answer 1

Depending on what the players try to do, you could call for saving throws and/or ability checks.

Saving throws are generally made to resist some consequence, and success means avoiding or reducing that consequence. Dexterity saving throws usually imply trying to move away, and Strength saving throws usually imply trying to not move.

Either could come into play here; perhaps the bridge sways, and you tell PCs near the edge to make a Dexterity saving throw to avoid falling off. Or a PC falls in the water, and you call for a Strength saving throw to not be pulled by the river's current.

Ability checks (or skill checks) are generally made when someone tries to accomplish some goal, and success means making progress toward that goal. If you want to give the players some creativity here, then consider that they may want to jump into the water anyway and swim across. Strength (Athletics) would be appropriate, or perhaps a different ability such as Dexterity (Acrobatics) for more dexterous characters. You could give advantage on the check to PCs who already have swim speeds, to reflect their innate swimming ability.

The skill could also vary depending on what the PCs are trying to do. For example, Stealth may be appropriate if they intend to swim quietly, or Nature or Survival if they try to find some calm path through the rapids.

The DC of the saving throw or ability check should not depend on the party's level, but instead be based on the nature of the task. The Basic Rules provide a table of Typical Difficulty Classes, and most moderately challenging tasks could have a DC between 10-20.

The consequences of failure are up to you. Is there risk of drowning? Do PCs in the current take damage from sharp rocks? Are they pushed back harmlessly? Remember that if the DC is high (20+), failure is more likely, and you should consider the severity of the consequences appropriately.

Answer 2

The athletics skill "covers difficult situations you encounter while climbing, jumping, or swimming" such as when you "struggle to swim or stay afloat in treacherous currents".

This suggests to me that you should ask your group for Athletics skill checks. If you definitely wanted to have them make saving throws instead, it should probably be in Strength. Either way, characters wearing heavy armor might receive a modifier -- advantage to resist being swept away, but disadvantage to resist going under the water.

The guidance for skill check difficulty is up to you, but the obvious choices would be 15 or 20. If you assign a 15, you should expect the group to generally get across the river; if you assign a 20, it's more likely that most or all of the group will be washed away, so you should think about what will happen next in the adventure if that happens.

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If I asked a group of eighth-level players to cross a 20-foot river, I'd expect one of these outcomes:

DM: "There's a 20-foot river."
Wizard: "I cast fly on the barbarian and he carries everyone across."

or:

DM: "There's a 20-foot river."
Druid: "I wild shape into a Giant Eagle and I carry everyone across."

or:

DM: "There's a 20-foot river."
Cleric: "I cast water walk and we walk across."

By eighth level, most spellcasting classes will have (and will have prepared) some sort of spell that will let them cross small obstacles.

Answer 3

It would be a Strength (Athletics) check to swim across.

There are two parts to this.

First, lets throw Dexterity away. Just looking at the situation before the rules, what does Dexterity have to do with resisting the current of the river? Even maintaining balance when attempting to wade through is a stretch. The only argument is that the force is from the side and the movement isn't directly against the current as it would be, say, walking into Gust of Wind. Looking at the Player's Handbook, pg 175 on Ability Scores, under Athletics:

You struggle to swim or stay afloat in treacherous currents, storm-tossed waves, or areas of thick seaweed. Or another creature tries to push or pull you underwater or otherwise interfere with your swimming.

Now, variant ability scores, of which I am a fan, would allow other abilities to use Athletics proficiency, but again, Strength makes more sense. The section on strength says it should be used when trying to "force your body through a space." Dexterity mentions "tricky footing" but this is resisting the force of the flow, not trying to walk on slippery, wet rock.

From the same chapter on pg 179, Saving Throws are to resist something done to the character, as opposed to Ability Checks, which are to resolve actions taken by the character.

A saving throw, also called a save, represents an attempt to resist a spell, a >trap, a poison, a disease, or a similar threat. You don't normally decide to >make a saving throw; you are forced to make one because your character or >monster is at risk of harm.

So while a Strength save might be appropriate to initially resist being swept away, a success leaves the character where they fell into the water. It would take a successful Strength (Athletics) check to swim across, and failure should probably result in being pushed downstream.