You can use a low-resolution texture for materials and let the pixel shader generate the material procedurally when viewed. An ice channel in the low-resolution texture can be added to a repeated high-resolution ice pattern and then thresholded. The same thresholding is used when casting shadows into the water. Multi-sampling the procedural function can create normal mapping for the light, but it's quite expensive.

The same method can be used with slightly different functions for other types of materials to get sharp detailed transitions between them. Just see the fuzzy interpolated amount of the material as the probability and the patterns as the random input. Multiple patterns can be added with different scale and rotation if it looks too repeated.