Just watching Modern Marvels (swords, axes and knives), and the the little factoid they share going to commerical was this:
A lot more swords are found in riverbeds than one would expect. No one knows why.
Has anyone ever heard of this?
Another fun fact: Most statements which are followed by “no one knows why” are just made up on the spur of the moment, with no relationship to truth. 
On a slightly more serious note, that statement seems a bit silly. If anyone knew why, then it wouldn’t be a lot more than one would expect, since we would then expect that many. And for that matter, how many swords does one expect to find in riverbeds? I must confess that it’s not something I’ve ever pondered, so I can’t say I really have any expectation at all. And if I may say so, I think I tend to ponder more and odder things than most of the population, so I doubt many other folks have an expectation concerning riverswords, either.
Stuff gets washed into stream, the stuff goes downhill.
Wouldn’t anything old and buried be more likely to turn up near a constantly eroding and meandering riverbed?
Certainly I recall seeing a number of archaeological documentaries where swords (among other items) were found in river beds or in mud dredged up from river bottoms.
A couple of hypotheses (that seem reasonable to me):
-You’re on horseback, crossing a river and you drop your sword into the water; unless it’s a crystal-clear stream, you’re unlikely to find it again; assuming you could even swim to get it if you could see it. Most likely it will sink a little into the silt on the bottom and be lost forever.
-You’re fighting an adversary near a river and you manage to disarm him; throwing his weapon into the water seems a good way to stop him retrieving it (at the same time as making sure it doesn’t become an encumbrance to you)
Why would you be fighting next to a river, or crossing it with your sword unsheathed? Rivers were more important to humans in the days before mains water supply - human settlements were clustered around them. They also often represented territorial boundaries - so you’re simply more likely to be near a river than anywhere else to begin with, and if you’re crossing it, you’re slightly more likely to be expecting trouble than otherwise.
IANAArchaeologist or historian, so take the above as nothing more than fanciful guessing.
I’m guessing it’s due to a lot of people pretending to be King Arthur and then drowning.
I remember seeing that on Modern Marvels because I thought it seemed obvious. It’s like wondering why coins are often found between couch cushions. When I saw the show a few years ago, I tried to find out if it was true. They do find some swords in riverbeds, but I didn’t find anything about how frequently or whether they knew why. There might be more online about it now.
As already mentioned, it’s probably because they fell into the water and either couldn’t be retrieved or it fell in unnoticed. Also, a sword that falls on the ground would have a high probability of being found by the owner or some other person. Hey, free sword!
Someone mentioned the sword getting washed into the river. I considered that, but in order to carry the sword, there would have to be a lot of water moving very fast. Unless it was already in a ravine, I don’t think the rain could carry it.
Perhaps the show’s creators just asked some guy who knew about swords why some were found in riverbeds and he said he didn’t know.
I go along with the theory Mangetout put forward. Rivers were very important in the past as a means of transportation of goods between settlements, hence many settlements appearing along coastlines and rivers (as well as the source of water for drinking and farming of crops). It is my assumption that if you were fighting a battle it would more than likely take place somewhere near a river, perhaps for control of a bridge that represents an important crossing point.
Well, you know all those watery tarts and moistened bints that wandered around old legends? They must have kept their stock of sacred weapons somewhere handy in case someone passes by, right?
This is my favourite explanation. Sure, more fighting might happen near rivers, but if a weapon is dropped anywhere else, it’s obviously going to get picked up.
That makes a lot of sense.
Here in Murfreesboro, a major part of the Battle Of Stones River was fought in Mc Fadden’s Ford, a place where horses could ford the river where there was no bridge.
Many men died trying to take that ford, & many bodies were not recovered. None of their weapons were.
In the pre-Industrial era, most weapons, usable or not, were salvaged from battlefield pretty quickly. Locals would get weapons to protect themselves from looters/pillaging armies/deserters/whatever. Or, to rebel. And broken weapons were salvaged as free metal, to be melted down & used for tools.
A weapon in a riverbed wouldn’t be found. Until much later.
Rivers are also much more likely to be battlefields because they’re a good defensive terrain feature to form a battle line on. Many armies would form up on a riverbank in order to fight an opposing army that was trying to cross the river and would be more vulnerable to attack while in the water.
And we have a pretty good idea why.
I believe this is the correct answer.
A local historian gave a fascinating talk about old local trails, roads, and buildings. He said one of their methods of finding them was to identify easy fords across streams and rivers–there was bound to be a trail there. And, since people were apt to get stuck there, there was bound to be a tavern nearby.
Swords + alcohol + river =
I think we have a winner 
But it’s good guessing, very nice guessing.
What you didn’t mention though, is fleeing from battle. If one is trying to run like hell through water, going back to find the sword you dropped is likely low on the list of things to do.
Hmm…what about the theory that things were thrown into rivers as offerings to the gods.
It was popular with the Romans and Celts as a form or worship. Perhaps some soldiers returning victorious from the battlefield would make an offering of their swords to the gods in return for victory and safe return?
Obviously more likely as an explanation with Bronze age swords, and less likely with ones from say, the American War of Independence.
A friend of mine just visited the dentist, and was told that she had something like 17 new cavities and would need 12 teeth pulled with as many root canals and implants. Needless to say, she was rather shocked at this, as just a few years ago she had pretty good teeth. When she asked the dentist why, he asked her if she drank a lot of Diet Coke. She does. He said something about the phosphorus causes massive tooth decay.
Question1: Is it possible for Diet Coke to cause so mach damage in such a short time?
Question2: Would any other diet sodas do the same thing? What about non-diet?