This could be someone having their fun with a jocular, easy-going academic botanist because it's sort of a bit too much of a coincidence for this to arrive in my email box on March 17th. A "curious student" asks: what happens to an aquatic plant if you put green dye into the water? Well, that is sort of interesting. Plants are green because chlorophyll absorbs wavelengths at the red-yellow and blue-purple ends of the spectrum of wavelengths that compose visible light, so the wavelengths transmitted or reflected will be green. Water dyed with a green pigment will do basically the same thing, so an aquatic plant in green water will get less light to absorb because more of the non-green wavelengths will be absorbed by the water than usual. Chlorophyll became the photosynthetic pigment of choice because if evolved in an aquatic environment where it absorbs those wavelengths that best penetrate water which is a great filter, and just in case you don't get the connection, land plants have an aquatic ancestry. And there's gobs of evidence that support that statement. One demonstration that my students perform is to shine light on a test tube full of some motile algae, usually Chlamydomonas, but the test tube has a black paper sleeve on it with little port holes each covered with a bit of colored cellophane, and one left just open. The algae have eye-spots and can respond to light, so when you remove the sleeve after a bit, there are bands of green caused by the migration of the algae to those port holes where they have accumulated to get the best light. So a red cellophane looks red because it absorbs the other wavelengths while red light passes through, and a pretty good band of green will be found next to the red light port hole, and so on. Now what will happen to an aquatic plant that finds itself in the Chicago River today? Nothing good! Yeah, if you didn't know this before, they dye the river green. Seriously.