Sundown

as seen from the east side of the river Great Ouse looking towards West Lynn. To orientate you the river goes off to the right to the sea (the Wash and North Sea), however at this moment the tide is coming in and the water is flowing to the left.

There are two tides a day and for each tide two points in time when the opposing flows are in balance and if there is no wind the water looks still and reflects like a mirror, "slack water".