Realistic rendering of underwater scenes is one of the most anticipated research topics in computer graphics. Caustics are the important component enhancing the realism of this kind of scenes. Unfortunately, rendering caustics is a time consuming task. As a result, most existing algorithms cannot handle this at interactive rate. In recent years, volumetric texture based rendering algorithms have been proposed. They can render the underwater scene with caustics in real-time. However, these algorithms require large amount of memory and are restricted to non-complex scene. In this paper we present a new interactive caustics rendering algorithm which require less memory usage. In our proposed method, we represent each object as a pair of color and depth texture. Color texture is used to store the object image viewed from viewing rays which refracted at water surface. We calculate the light intensity distribution on this image and store the result back to the color texture. The depth texture is used in the intensity calculation process to improve accuracy of the caustics patterns. Our experiment shows that proposed algorithm can handle complex underwater scene with caustics at interactive time rate. While using a pair of color and depth in stead of volumetric texture, we can reduce memory usage significantly.