I usually go everywhere on foot. When I come to a river I just swim across. Recently I decided to ride to the next village and equipped my horse with diamond armor. When we came to a river I thoughtlessly rode into it, just like I do when on foot. Suddenly my horse was gone and I never found it or its armor and saddle again. It came as a shock without warning. I thought that if the horse was in trouble I would notice its distress, but no. I can’t remember if I thought to press T to see any on-screen messages that may have appeared.
In my experience, usually you will be dismounted from one once in water that's too deep (two or three blocks?) for them, and they will typically attempt to swim towards the closest shore (so crossing a wide river can be a pain as they keep trying to go backward). For it to have immediately disappeared is strange though.
I do believe they can drown though (they can definitely suffocate in walls); another player in my world once lost their horse in a river. It had a ravine cutting under it with water flowing down, so I'm not entirely positive if it fell or drown, but I want to say the player retrieved the horse but lost it due to drowning attempting to get it back up. If they can't drown then I am remembering wrong and it must have fallen.
Since the horse simply disappeared without a trace it was likely due to the following bug, present since at least 1.9 and fixed in 1.15 (I've never experienced this, at least not with boats, which are said to have the same issue):
Note that it didn't actually disappear, it just isn't being loaded and/or rendered client-side (I've seen this when watching a video and it came back when they relogged. Some of the comments on the bug report say that if you do not immediately reload the world it can be lost forever).
In either case, I highly doubt that a horse can drown from simply riding into water; most mobs will automatically swim to the surface and only flowing water, such as a waterfall, or a bubble column (only in oceans) may catch them in a way as to make them drown (there have been past issues with small mobs drowning because the game thinks their head is underwater; until I fixed it baby chickens in particular would always drown, but I've never seen adults drown).
Since the horse simply disappeared without a trace it was likely due to the following bug, present since at least 1.9 and fixed in 1.15 (I've never experienced this, at least not with boats, which are said to have the same issue):
Note that it didn't actually disappear, it just isn't being loaded and/or rendered client-side (I've seen this when watching a video and it came back when they relogged. Some of the comments on the bug report say that if you do not immediately reload the world it can be lost forever).
In either case, I highly doubt that a horse can drown from simply riding into water; most mobs will automatically swim to the surface and only flowing water, such as a waterfall, or a bubble column (only in oceans) may catch them in a way as to make them drown (there have been past issues with small mobs drowning because the game thinks their head is underwater; until I fixed it baby chickens in particular would always drown, but I've never seen adults drown).
That seems to make the most sense in my case. If I was automatically dismounted as described by Princess_Garnet, the bug could be the cause of the instantaneous disappearance of the horse. Unfortunately, it didn‘t occur to me to re-load the world, but I was more concerned about understanding why it happened than about getting the horse back, so I am satisfied. It is just too bad that it was such a fast horse - the fastest I had ever tamed.
I do notice some quirks with horses appearing when I play with other players on my world though LAN (this may extend to multiplayer but the extent of my multiplayer is LAN so I don't know). Either the horse appears, but the player riding it does not, or sometimes it's even the other way around. This usually tends to occur when a player comes within render distance on a horse already (as in, if we both mount the horse within range of one another, it typically works fine, but once someone leaves and re-enters, the result is random).
I think maybe once or twice another player will have dismounted their horse (willingly) and then claim they can't see the horse, and have to leave the world then rejoin to see it (I would be able to see it though). But never has anyone been forcefully removed from one, outside of it occurring due to entering water that is too deep or something.
Since single-player is multi-player without the extra players (that is, single-player runs a server that you connect to), I guess the same could happen there. I've just never had it happen when it's just me (and even when it happens, it's just them visually not showing sometimes; never been forcefully dismounted outside of trying to tame a wild one). Probably because it only seems to be a visual bug that occurs when involving leaving and/or entering render distance of another player, and in single player, you can't do that haha.
I usually go everywhere on foot. When I come to a river I just swim across. Recently I decided to ride to the next village and equipped my horse with diamond armor. When we came to a river I thoughtlessly rode into it, just like I do when on foot. Suddenly my horse was gone and I never found it or its armor and saddle again. It came as a shock without warning. I thought that if the horse was in trouble I would notice its distress, but no. I can’t remember if I thought to press T to see any on-screen messages that may have appeared.
In my experience, usually you will be dismounted from one once in water that's too deep (two or three blocks?) for them, and they will typically attempt to swim towards the closest shore (so crossing a wide river can be a pain as they keep trying to go backward). For it to have immediately disappeared is strange though.
I do believe they can drown though (they can definitely suffocate in walls); another player in my world once lost their horse in a river. It had a ravine cutting under it with water flowing down, so I'm not entirely positive if it fell or drown, but I want to say the player retrieved the horse but lost it due to drowning attempting to get it back up. If they can't drown then I am remembering wrong and it must have fallen.
Since the horse simply disappeared without a trace it was likely due to the following bug, present since at least 1.9 and fixed in 1.15 (I've never experienced this, at least not with boats, which are said to have the same issue):
MC-101247 Horses, donkeys, mules, and boats sometimes disappear after dismounting
Note that it didn't actually disappear, it just isn't being loaded and/or rendered client-side (I've seen this when watching a video and it came back when they relogged. Some of the comments on the bug report say that if you do not immediately reload the world it can be lost forever).
In either case, I highly doubt that a horse can drown from simply riding into water; most mobs will automatically swim to the surface and only flowing water, such as a waterfall, or a bubble column (only in oceans) may catch them in a way as to make them drown (there have been past issues with small mobs drowning because the game thinks their head is underwater; until I fixed it baby chickens in particular would always drown, but I've never seen adults drown).
TheMasterCaver's First World - possibly the most caved-out world in Minecraft history - includes world download.
TheMasterCaver's World - my own version of Minecraft largely based on my views of how the game should have evolved since 1.6.4.
Why do I still play in 1.6.4?
Well I mean
probably ¯\_(ツ)_/¯
wack
That seems to make the most sense in my case. If I was automatically dismounted as described by Princess_Garnet, the bug could be the cause of the instantaneous disappearance of the horse. Unfortunately, it didn‘t occur to me to re-load the world, but I was more concerned about understanding why it happened than about getting the horse back, so I am satisfied. It is just too bad that it was such a fast horse - the fastest I had ever tamed.
I do notice some quirks with horses appearing when I play with other players on my world though LAN (this may extend to multiplayer but the extent of my multiplayer is LAN so I don't know). Either the horse appears, but the player riding it does not, or sometimes it's even the other way around. This usually tends to occur when a player comes within render distance on a horse already (as in, if we both mount the horse within range of one another, it typically works fine, but once someone leaves and re-enters, the result is random).
I think maybe once or twice another player will have dismounted their horse (willingly) and then claim they can't see the horse, and have to leave the world then rejoin to see it (I would be able to see it though). But never has anyone been forcefully removed from one, outside of it occurring due to entering water that is too deep or something.
Since single-player is multi-player without the extra players (that is, single-player runs a server that you connect to), I guess the same could happen there. I've just never had it happen when it's just me (and even when it happens, it's just them visually not showing sometimes; never been forcefully dismounted outside of trying to tame a wild one). Probably because it only seems to be a visual bug that occurs when involving leaving and/or entering render distance of another player, and in single player, you can't do that haha.