The predominant round-leafed plant is pennywort (aka dollar-weed when it grows in your lawn). The other intermixed plants are probably alligator weed, primrose or smartweed - or a combination thereof. Your wide-angle photos don't permit close-up inspection to specifically ID the other plants.
Aquatic-labeled formulations of glyphosate, 2,4-D, triclopyr or imazapyr are effective on all of the listed species. Other factors, including water-use restrictions that are relative to your pond's primary or secondary purpose, may dictate which of these chemistries is most appropriate for your needs.
None of these herbicide formulation are expected to have any adverse effects directly on resident fish, but treating/killing too much weed growth at one time can create a fish-lethal dissolved-oxygen decline due excessive bacterial decomposition of the treated biomass (which utilizes available oxygen).
