Watershed line

Water from the right side, coming from upstream, is dirty due to just started precipitation.
EXIF Information extracted from file:
DateTimeOriginal: 2006:06:24 13:21:26
Camera Make: Canon
Camera Model: Canon PowerShot A510
Exposure Time: 1/500.0 seconds
FNumber: 4.0
ExposureBiasValue: 0
MaxApertureValue: 2.6
MeteringMode: center-weighted
Flash: Flash did not fire, auto mode
FocalLength: 5.8125 mm