Making ice is fun and not all that hard. So why do I find so much bad ice in-world? Here's the secret. Make the whole prim invisible (use the *Default Transparent Texture from the basic Inventory), then texture only the surface with the "ice" texture of your choice (I like Waterfall - dense layer 1 in the basic Inventory). If you use more than one prim to make a larger size body of water, adjust the repeats and offsets so that the joins are seamless ... not doing this is the biggest mistake I see for in-world water, frozen or not). Then make a bed for the water. Most any rock or dirt texture works well. This prim will be immediately under the ice so folks looking through have something to see. If you use a more opaque ice texture you can skip this step.
Yep. All that in the preceding paragraph is a bit vague, but the idea is to get you in the ballpark and playing with ideas. Stop by my store (SLurl) and grab the free Creating Ice in SL® Tutorial box to learn more ("buy" it for L$0).