Absolutely nothing to worry about. The large plant floating in the open rectangle is Pistia stratiotes, or Water Lettuce. Some data below from my profile if interested. The smaller floater is Salvinia, not sure of the species but probably S. molesta [data on this below too]. My plants looked much the same for years. Interesting thing about our water now (we have the same municipal water) is that my plants took a decidedly down turn when they increased the soda ash to increase the pH to 8-something. They remained alive, but never with the same shine.
Salvinia
Salvinia is a small floating fern, the sole genus in the Salviniaceae family. It consists of three leaves, two floating and one modified leaf submerged that may be mistaken for a root; the stem is branching and creeping, bearing hairs but no true roots.
This plant likes bright light; in its habitat it occurs in full sun. It also requires good nutrition from the water, and there should be good air circulation. The two surface leaves, which are larger than those of Duckweed, are green or sage green in colour, with a beautiful silvery sheen; these leaves will turn brown and melt if conditions are not satisfactory.
Salvinia auriculata is the species often associated with the aquarium plant, but several authors believe this is inaccurate. Kasselmann (2003) suggests that S. molesta is the species most often found in aquaria, and according to Mitchell (1972) is likely a natural hybrid of S. auriculata and S. biloba. S. molesta was described in 1972 by D.S. Mitchell; the species epithet is Latin for damaging or bothersome.
Pistia stratiotes
Variable. In good conditions, this plant will grow large, up to 50cm / 20 inches across, though usually smaller. Growth depends upon conditions. The so-called "Dwarf" Water Lettuce is not a distinct species but simply due to less-than-ideal conditions of light and nutrients. A magnificent floating plant that is best suited to an outdoor pond or large aquarium. The "dwarf" form, which is not a separate variety, subspecies or distinct species, is believed by most sources to be due to less than ideal conditions; observations have noted that the "dwarf" plants develop into normal large plants when conditions improve.
The species was described by Carl Linnaeus (1707-1778), the Swedish scientist who developed the consistent use of binomial names for both plants and animals that we use today to classify all life, and who himself validly published over 9,000 plant names. Linnaeus erected the genus Pistia, the name derived from the Greek pistos, meaning watery, which contains just this single species. The species epithet stratiotes is Latin and means reminiscent of the Stratiotes genus of submerged aquatic plants.
