So theres a whole bunch of bees on the water hyacinth. why?

we got a fish pond outside, with lots of water lettuce and water hyacinth on it. theres a whole bunch of bees that are always hanging around the pond. they land ONLYon the hyacinth. the hyacinth is NOT blooming, and the bees are NOT drinking. what is the problem here? iev heard taht they are there for the flowers and to drink, but both are incorrect. help?