It's another flower from Morning Glory family(Convolvulaceae). It has different names around the world, Water Spinach, Water Morning Glory, Water Convolvulus, Swamp Morning Glory, Kolmi Ful(কলমি ফুল), etc. Botanical/scientific name of the flower is Ipomoea Aquatica. Unlike other morning glory flower, this one used to grow at fresh water and used to grow very fast.
Its a perennial herbaceous trailing vine and cannot grow at low temperature region. This vascular plant can grow equally at the water and at the bank of water area(or moist soil). The color of this flower is bright white and shaped like a funnel. Other characteristics are similar to other morning glory flowers.
We can use this plant as vegetable and its very palatable. At some countries people cultivate this to feed the cattle and pigs. At most of the countries, this is considered as a noxious weed and almost impossible to eradicate. The seeds can be dormant for approximately 30 years. Also it will grow at next year even from a tiny amount of root(if exists). More of this plant is available at WikiPedia.