I tried really hard to Google up a picture but was unsuccessful. But in the park near my work, there is a pond/lake with ducks and small fish in it. There are also a couple of large metal baskets sticking up out of the water near the middle of the pond. They resemble Frisbee golf baskets (like this but more bowl shaped). They always are empty when I have seen them.
My question is, what is their purpose? Somewhere for large water fowl to build nests?
Is the pond lined with concrete? If so, such baskets might be used to anchor or suspend large water plants like irises or lilies.
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Something like this (upper right) or this? If so, that’s a grating to prevent large debris from washing into the pond’s outlet structure.
ETA: ok, so they’re probably something different. Maybe something used to break up the water surface for aeration or algae reduction?
Are there fountains in the pond that are just turned off?
When I was a child, ponds lined with concrete were typically called “pools”.
This was my original thought, and your second link, top picture most closely matches what is out there. But I never see any evidence of nests in the baskets.
Definitely not a grate. You have water surface, about a foot or two of pool, and then a basket made of chain on top of that.
It is a cement pond, but in the 3 years of hanging at this park, I have not seen one plant in the baskets.