What's the pink powder?
Personally, I really, really like Conibear 330's for beaver. Set them in the run that they use by their den, either in the bank or the beaver house. As close as possible to where they come out. Make sure they are firmly placed on the bottom, and I use a stick either pushed thru the coil of the spring, or inside the jaws to help keep them in an upright position. At times I'll use a stick to help direct the animal down to make sure it swims thru the trap and not over it. Make sure that you use wire and wire the trap chain to a large branch or something that won't move. Even tho the traps kill the critter, they can still struggle for a bit and will run off with the trap if it's not anchored.
Otters can be trapped using foothold traps at the bottom of where they slide into the water, or if the depth of the water permits, I'd set a 330 there as well. Placing a stick on top of the water to make the animal dive down to go under the stick and thru the trap.
Rex, ewest does a good job on beavers as well with the 330's.
Just be careful with the 330's. There is a setting tool available that will help you compress the spring. If you've never used them before, and don't know of someone locally that can show you how to use them, I'd buy a conibear 110 and practice setting and placing the trap before jumping up to the 330's. The 110's are used for muskrats. While the 110 will hurt if you slip and let it snap on you, the 330 might very well break a bone. You wouldn't want to set a 330 above ground if you have any pets running around.