In a recent discussion of Teva sandals and the like, it came up that serious river guides use ones that have buckled straps rather than velcro, because the velcro doesn’t hold well when it’s wet. This is the first I’ve heard of this, and I haven’t noticed my velcro Tevas spontaneously releasing in water, but you never know.
Is it true, and if so, why?
Water lubricates the hooks and loops.
I have a pair of Teva sandals, and another pair of Teve-like sandals. I’ve never had any problems with the Velcro releasing in water.
The Velcro on my SCUBA gear works fine as well.
It’s likely only a problem with cheap velcro, where the hooks and loops are too thin and flrxible for the purpose it’s put to.
Weird. I had some velcroed sneakers that I couldn’t get to fasten when they were wet, but they would not spontaneously cut loose if they were already fasetened and then got soaked.
My old Tevas released consistently when wet. I’ve used rubber bands for years to slip the end of the strap under which keeps them in place.
I bought new Tevas last week…they hold up well in the water. I’d guess the older the velcro is (the more used it is), the more likely there is going to be a problem.
Velcro doesn’t work when one or both sides are full of mud. Muddy buckles work fine. River guides get muddy. So…
My 2 year old leather TEVAs hold up just fine on my nightly swims in the pond.
I’d go with the mud issue.
Velcro seems to wear out over time, as the loops get frayed and the hooks get compromised. The more it is used (river guide wearing the same sandals every day, all summer; scuba guides who are in and out of their gear all year, etc.) the faster it’ll wear out.
I’m sure that if this is true, it depends on the type of velcro. The velcro straps on my waterskis always seem to work fine when wet. 
I’ve got some Tevas that are about six years old and the velcro’s gotten to the point where it’s a gamble whether the stuff will stick at all. Whether the hooks are all broken, or the loops are all broken, I don’t know. I’ve got replacement velcro, but just haven’t had the time to mess with it.
Been wearing firefighting gear for years, and the storm flap behind the snaps is velcro-works just dandy wet and dry.