It is very easy to look into ponds and lakes, even slow moving rivers, and see a lot of leaves on the water's surface and yet take no notice. If there were bright yellow or large white flowers we would take note; "what lovely water-lilies!". But just, apparently, leaves; who is interested?
These leaves can be produced by a number of plants but the pondweed family are responsible for many and as such are appropriately named. The broad-leaved pondweed (Potamogeton natans) is one of the most common species and has rounded green leaves, smaller than a water-lily but much larger than a duckweed. It is not just leaves, however, as it produces a few stout spikes of pale yellow flowers but the leaves still seem more conspicuous than the flower stalks.
There are several pondweed species, few are common and some are escapes from water gardens so in fresh water ponds and lakes the most likely one you will encounter is the broad-leaved pondweed.