Taking a summer break from Next Exit History, I am temporarily reverting to "Where in Hudson Is This," and giving the answer in the same column.

Walkers may have noticed that occasionally the water level in the ponds behind the Barlow Community Center on S. Oviatt Street is dramatically lowered.

The city adjusts the water holding capacity as part of Hudson's flood control, when heavy thunderstorm activity is expected. Several weeks ago it was almost drained (always enough water to support the fish and wildlife) and my walking buddies pointed out these interesting forms.

Happily Tom Munn, Hudson's Public Works Superintendent and Arborist, knew what they were. They are fish nests; males build them to attract females, hoping to impress them with their building prowess.

Frankly, these examples are quite dull and boring compared to some of the amazingly intricate architectural designs found in a link provided by Munn. http://webecoist.momtastic.com/2012/10/02/carp-circles-seven-fantastic-oceanic-fish-nests/ Munn guesses that the ones pictured are bluegill/sunfish nests.

Typical spawning occurs April through June, so the fish hatched and these nests were long abandoned before the ponds were lowered.

I've always found it interesting to stand on the little bridge and stare at what is uncovered when they drain the ponds.

Two years ago it was hundreds of mussel shells. If you're a long-time reader of my column you may remember that mussels, in egg stage, are taken into the mouths of fish, and then attach to the gills. There the mussel egg remains for up to six weeks, not getting larger, but developing adult characteristics.

Barlow Ponds are stocked with fish, and some of these apparently brought in the mussels, who drop off at the end of the third stage of their development and, finding a suitable environment at the bottom of the ponds, grow into adults. Odd that this year I saw no mussel shells. Wonder what will appear next time the water level is lowered.