Compare these two with how they looked in September. The one on the left grew rhizomatously, and as you can see is showing signs of greening up for spring. I took this photo a few days ago, and had another look this evening. To the right of these two, on the southern end of the middle pond, there are 4 or 5 new plants, just breaking the surface of the water, which look as if they are new rhizomatously produced T. latifolia.
I know it might sound a bit odd to welcome a plant which is said to be invasive, and is shaping up to be so. But there's nothing growing in the pond which is all that interesting, apart from these. (I did want to grow water mint, but... I have either mislaid the seed packet, or actually sown them in the pond, and forgotten about it). There's a dock which survives despite being under water most of the time; various grasses and mosses.
Whatever happens, I'm not going to be proactive with the pond for this year at least. Too much else to do, so let's see what happens.