When the player is on a water space, track whether they are submerged or swimming on top of the water. By default, entering water without the risk of drowning still puts you at the bottom, but you can use < to ascend to the top.

A primary effect of this is to establish consistency with what you can and can’t interact with while in water - it doesn’t make much sense that monsters standing on an adjacent land square, or monsters flying on an adjacent water square, can hit you in melee when you’re underwater, nor the other way around. If being on top or bottom of the water is tracked, these cases can be prevented, but care would have to be taken so that the hero can’t dive underwater and be completely safe and able to recover with impunity.

One possible mitigation (in addition to blocking an underwater hero from using melee attacks on adjacent monsters that aren’t in the water themselves) would be to make monsters that can’t currently attack the swimming hero avoid getting into melee range. Though this still wouldn’t deal with zapping them with spells from a safe distance.

There are adverse effects if you swim within a certain amount of time after your last meal, because of the traditional advice that it’s dangerous to swim less than an hour after eating.

Artifact cloak Mantle of the Manta Ray, inspired by a similar D&D cloak. It confers magical breathing and swimming when worn.

Wearing sea dragon scale mail grants extrinsic swimming.

If you have swimming, you can use , to pick items up from underwater.

New artifact: The Trident of Poseidon. Chaotic (only because Poseidon is in-game). While carried, grants magical breathing, swimming, and protects items from water damage. When wielded, confers water walking. Double damage versus aquatic monsters, and gets a damage bonus versus all that scales with the amount of water squares adjacent to you. Invoke to get an UnNetHack-style flood.

Swimming skill: how well you can swim on top of water and carry weight at the same time. At Unskilled you can carry very little, but it quickly increases beyond that.

Swimming while satiated can cause you to drown from stomach cramps.

Give some monsters the M2_SWIM ability: rats, possibly dogs, possibly horses.

Tourists should be able to swim. Alternatively, tourists should specifically NOT be able to swim, but other roles might.