Building a raised wall for a pond
This website has a good explanation of hydrostatic forces on a dam surface. You could build your wall with a submerged lip to help counteract the moment applied by the water pressure on the vertical face of the wall.



Image from TheConstructor.org

I did some quick calculations and got the following:


So to sum up my incoherent scribblings, assuming a 30 lb cinder block holding back 8" of water and a coefficient of friction between the ground and the blocks of 0.4 (which I think is conservatively low), the blocks will not tip, but they will be pushed backwards by the hydrostatic force.

Reducing the water level to 6" results in the wall being able to withstand the hydrostatic force by a small margin. Even so, you'd be risking high water conditions after a heavy rainfall destroying your wall. It will need reinforcement. You could do that by pouring concrete into the voids and increasing the weight of each block to greater than 46 lbs. You could also drive a rebar stake on the inside of each block against the side holding back the water.

NOTE: I did quick calculations and made a lot of assumptions. This answer is an estimate and should not be considered professional advice. (Translation: Please don't get pissed off at me and track me down if your pond floods your yard.)