I am building a small waterfall in my backyard. Would like to know easiest and safest way to run power for the pump. There is a plug in about 10 yards away.

Assuimng you need a 20 amp 120 volt circuit, you need to dig a trench, install either 1/2" or 3/4" PVC Schedule 40 conduit from existing outlet box to new outlet box, pull 3 - #12 THHN/THWN conductors, one black, one white, and one green.

I will assume the existing outlet is already GGFI protected.