I played a game of Carcassonne last night with some friends, using amongst other expansions, the river.
Their "house rule" was that both the river Source and Lake tiles do NOT wrap around: on each tile there was a corner that they designated a boundary between one pasture and the next. I'm pretty sure that in my edition of the rules it specifies that these tiles DO wrap. But I'm not a rules lawyer, I'm perfectly happy to play a variant, as long as it's clearly stated from the outset!
They had another rule for playing with the river, though, and in this case I realize I have no idea whether it's "official" or not: neither the Source or the Lake tiles counted as a "turn", so in both cases no meeple could be placed, and the player whose turn it was drew another tile.
Does anyone know for sure whether the Source and Lake tiles "count" for the purposes of taking a turn? (I can't even remember whether the starting tile from the basic game "counts", right now...)