Are there any snails in your pond? That might me what they were after.

If I had to guess I would say that the pond temperatures are going up and the watercress has died back for the summer. I know my watercress in my pond has died back. When it did it died back fast. But it will be back this fall and next winter I will be pulling 50 lbs every two weeks out of the stream.
Mike

Oh, so it likes cool weather?

No it loves cool or cold weather. If you can keep it in unfrozen water it will stay green all winter and grow like crazy.
Mike

Thanks for that info mike.

I have grown watercress for years and yes it does prefer cooler temperatures, but it does not die back in the summer here and we have hot summers. It becomes slightly "woody" with thick stalks and lots of leaves. If you plan to use it in salads etc, the leaves from the tips are best during summer.
Some people grow mustard cress thinking it is True Watercress (Nasturtium officinale).
"Horton"

Here is a link that might be useful: Watercress Nasturtium officinale

Is it safe to assume the grocery store 'watercress' is true watercress? I bought some a week ago, placed it in the top of the waterfall as well sticking pieces out from rocks (with the stems in the water) and it definitely rooted fast, within 6 days. The price was right.

Tonight I saw three Blue Jays splashing around in the top of the waterfall among the watercress, though I assume all they were after was a drink of water and a bath (the watercress didn't look at all harmed).

I've never noticed so many birds visiting the pond since I redid my waterfall.

Glen

Glen, you would hope so, but since many people had never even heard of True Watercress, prior to having a pond or knew you could use it in salads, etc, you never can tell what a store may put out there and call it Watercress.

The cress family has many variants, most are edible, some like to grow in water some do not.
"Horton"

Here is a link that might be useful: Cress information.

Is it safe to eat plants grown in the pond or bog?

I think its probably not coons because when I made a floating island, they tore it to pieces the 2nd night. You would know if your pond was covered in styrofoam 'snow'. Min