Parkside Pool is Cambridge's largest and is on Gonville Place (next to the open area of Parker's Piece, in the south-east of the city centre). It replaced an older pool that had stood here for 30 years. Apparently, this mosaic was saved from the old building and installed in the new one.
The mosaic in the reception area shows the coat of arms of the City of Cambridge. The three ships sailing by on the shield seem to strike a chord with the Christmas tree in the foreground.
The "Neptune's Horses" are reminiscent of the half-fish seahorses of a Roman thiasos (a parade of marine creatures, often shown in mosaics) - here's an example of a thiasos. The pictures below show details of the seahorse's scales and the ships.