This is indeed the IJ which is an ancient piece of water dividing Amsterdam into a northern and a southern part (would not call it a river because it is stagnant) , just visible before the bow in the distance is the now called Damen Oranjewerf Shipyard, not to be confused with the much larger Damen Amsterdam yard (former NDSM) which is in another part of the IJ.

This is Amsterdam.

Is that a Dutch courtesy flag? If so the location could be in the Ij at Amsterdam, at the "Engelse Boeien" (English buoys), which were regularly used for lay-ups.

Great shot! More of them. Thanks for sharing.