This mod introduces the item "Staff of Moses", which can be obtained with the help of a burning bush.
With the staff equipped, right-click in the direction of water will create a passage to a dramatic music cut from "The Prince of Egypt"; right-click in any other direction or logging out will close all passages. One passage is maximum 5 blocks wide and 64 blocks long (it is now configurable); it may be narrower if the coastline is irregular (I might fix this someday).
Hit stone with the staff to create a source of water.
Left-click water to turn all water around into blood and back.
As people have suggested, there is now a staff that parts both water and lava.
This mod should work in single player and multiplayer.