I need to get the skum out of the bottom of my pond, but I have no where to put the fish, so I'm thinking vacuuming is out of the question. Does anyone have any good ideas?
It's only about 500 gallons and the water is clean, but I can see accumulated debris at the bottom.

In the wild this would be a normal situation in a pond. You may want to physically remove the debris using a long handled net like they use for swimming pools. You really don't want to remove too much of this bottom material as that means your pond is essentially alive and your fish are doing just fine. Removing too much of this may actually disrupt your mini ecological area and end up killing your fish as a result. Having outdoor ponds with fish in can sometimes be hard to properly balance.

A friend of mine had huge (I'm talking 500 gallon indoor) tanks that were literally covered on the inside with green algae. I asked her why she didn't clean off the algae as it looked awful. She explained to me that if she did do that her tank would be "dead" and the fish would die as well from the lack of the natural algae. She was a discus breeder and discus are very fragile and hard to raise fish in captvity, but don't tell her 4 huge tanks that!! They were all crusted over with the green algae and were all very healthy.

A pond company would catch the fish and stre them in their native water in a large tank while they drained the pond and power washed it. You can get moderate success by using a wet shop vac. Once the tank fills you unscrew the drain cap and let all of the water and debris drain to the ground, if you snagged a fish it will pop out and flop around. You can return them to the water with not harm. They charge $250 to clean my 1000 gal pond.

Are you saying that if a fish gets sucked up into the shop vac, it will be OK? WOW! What a ride. I'll try that method.

A small fish can pass down the vac pipe without any real harm, the smaller the better.