Beware of plants from outside sources.
That plant is definitely a terrestrial weed & the picture you took clearly shows it's located right next to the sewer grate.
Based on the details in that photo you posted, I can see a zinc plated hex bolt, several lava rock type stones, and other miscellaneous debris you would find in a urban sidewalk.
Weeds can grow ANYWHERE & can absolutely THRIVE on pollution too. Make sure you don't grab stuff that's from water, that could be contaminated with antifreeze/oil/detergents/surfactants.
Various types construction waste & oil slicks in the surface of the water is a good indicator to disqualify the source.
If you drop in the wrong plant, it's a great way to kill all the CHERISHED inhabitants of the tank and introduce a huge spectrum of unwanted parasites & other deadly pathogens.