vcmi/config/rivers.json

{
    "waterRiver":
    {
        "originalRiverId": 1,
        "code": "rw", //must be 2 characters
        "animation": "clrrvr",
        "delta": "clrdelt"
    },
    "iceRiver":
    {
        "originalRiverId": 2,
        "code": "ri",
        "animation": "icyrvr",
        "delta": "icedelt"
    },
    "mudRiver":
    {
        "originalRiverId": 3,
        "code": "rm",
        "animation": "mudrvr",
        "delta": "muddelt"
    },
    "lavaRiver":
    {
        "originalRiverId": 4,
        "code": "rl",
        "animation": "lavrvr",
        "delta": "lavdelt"
    }
}