Question
I want to enlarge my current pond which is about 3 feet deep, 8 feet wide and 6 feet long, all under the ground.  I would like to build a pond wall, about 2 foot high above ground, to increase the depth of the pond.  And possibly making it a little larger also.  Will the no mortar retaining wall blocks be able to hold the weight of the water if i install them with a pond liner?  

Answer
I'm not familiar enough with the sturdiness of the exact wall blocks you might be considering using.  The pressure on the blocks will depend on the depth of the water above ground.  You can use cinder blocks with mortar or wood (2 x 4's and such) to make the wall as long as an underliner (cloth or something) and liner are used over that.  As for the loose wall blocks, I don't know if I'd trust them to stay in place.

Good luck!
Robyn
fishpondinfo.com