Prismarine is a shaderpack that absolutely blew my mind. It is Capt Tatsu's edit of the BSL shaderpack. Prismarine contains all the features of BSL and also contains new colours and visuals. The volumetric lighting, volumetric fog, distance blur, nether heatwave and smoke make up for a very realistic looking game. The pack offers a freedom of customization - almost everything can be directly modified in game. The pack will run well on mid-end to high-end PC's. Furthermore, there's per-biome fog, weather and sky. Prismarine will work with both Iris shaders and Optifine.
Download links are given below.
Follow the procedures described below to install this shaders into your game
1) Install latest version of Optifine
2) Download the shaders
3) Move into .minecraft/shaderpacks folder