diff --git a/terranostra.lisp b/terranostra.lisp
index cfc8ab3..0e647bb 100644
--- a/terranostra.lisp
+++ b/terranostra.lisp
@@ -110,8 +110,30 @@
 
 (defun create-stream (x y world)
 	"Create a stream, starting at x/y"
-	;;TODO
-	)
+	(let ((dir NIL) (min 10000) (nextpatch NIL))
+		;;XXX min=1000 is is a hack to get a hypothetical maximum altitude
+		;;Figure out the lowest neighbouring patch
+		(dolist (d *directions*)
+			(let ((np (patchindir x y d)))
+				(when (and np (< (patch-alt np) min))
+					(setf min (patch-alt np))
+					(setf dir d nextpatch np))))
+		(unless (and dir nextpatch) (return-from create-stream world))
+		;;Set streams-in and streams-out
+		(setf (patch-streams-out (coord x y))
+			(append (patch-streams-out (coord x y)) (list dir)))
+		(setf (patch-streams-in nextpatch)
+			(append (patch-streams-out nextpatch)
+				(list (opposite-dir dir))))
+		;;Erode this patch
+		(setf (patch-alt (coord x y))
+			(- (patch-alt (coord x y))
+				(random (round (/ (patch-alt (coord x y)) 10)))))
+		;;Continue forming the stream
+		;;FIXME causes an endless loop -> lowest neighbour becomes this patch
+		(create-stream (first (patch-pos nextpatch))
+			(second (patch-pos nextpatch)) world)))
+
 
 ;; Initialize the random state (which would otherwise not be very random...)
 (setf *random-state* (make-random-state t))