This photo from 1955 shows that there was more than just waiting and sailing in the lock. The caption in the image bank of the municipal archives reads:
'Water polo match in the lock chamber in front of the Grote Sluis. In the background, buildings on the lock island and the Oostzijderkerk in the Klauwershoek.'
The photographer must have stood on a kitchen stair, with his back to the old post office. He had a good view of the event. Many people have come to watch. It must be a special event, because the swimming pool in the Voorzaan on the ferry island is nearby. Could anyone tell us why the lock chamber was diverted into a swimming arena? Did that happen often? Or was it a one-off demonstration competition to attract new members for the Water Lily, the women's section of swimming club Neptunes? I wouldn't be surprised if there were more competitions in front of the lock gates: the dimensions are ideal for water polo and the floating walkway to which the goal is attached looks professional.
The moment the shutter moved is well chosen. The player with the dark swimming cap fires at the right goal post intersection, while she keeps her opponent at a distance with her left arm. Smart foul but no goal. One of the, somewhat numb, substitutes across the water looks on in shock. The umpire, in shirt and tie, doesn't flinch.
It couldn't have been very pleasant. Not only is it a little too cold to swim in open water, it's also not without health risks. For many years, all kinds of polluting industries have been freely discharging waste water into the Zaan. In the mid-1960s, the swimming pool in the Voorzaan was closed and demolished because of the very poor water quality. It wouldn't have been much better ten years earlier.
Lock keeper
EN 
NL