Minecraft wiki entry for Water, associated text: The horizontal current in a water block is based on a vector sum of the flows to and from that block from its four horizontal neighbors. For example, if a block receives water from the north and sends it both south and east, but borders a solid block on its west edge, then a south-southeast current exits from that block, because 2 southward flows (in and out) are combined with 1 eastward flow (out). Thus, 16 horizontal directions are possible. If a branch in a channel is 2 blocks wide at its entrance, then entities float into it rather than continuing in a straight line.