I walked down a stream about 3 weeks ago, Putah Creek near Davis, CA.
Creek is fairly clear water in most sections. I needed a certain species of weed propagules for an experiment. So bucket and boots in hand, down the stream I go.
Some sections were covered with long Spirogrya and diatoms so you could not see anything below, roughly 10-20cm deep from top of the water to the bottom.
right next to this, the plants were growing and clean without algae. Further down, some plants were matted with algae, further down, no algae on one section of the stream, but across on the other side, lots of algae of various species.
Down farther, a shallow section had Vaucheria algae, some bright green attractive Pithophora and some encrusting greens and diatoms on the rocks.
Next to this in slightly deeper water was a good deal of the plant propagules I wanted.
I pulled them up and they were clean as a whistle.
You could walk up and down this stream and find no less than 6 different species of (angiosperms) aquatic weeds. Some sections had been covered with hair algae, others were absent of any plant growth or algae, other sections were full of clean healthy growing aquatic weed beds.
Nutrients in the water column explains zero correlation here.
Light? Perhaps, but the far side is shaded, but the sunny side gets the same/similar light up and down the creek most of the day.
Velocity of the flow/currents/seasonal timing of the observation(hardly any hair algae in the winter), sediment type(this is deposited based on water flow/currents), scouring, bends in the flow of the stream.
Still, there are many good examples in and within aquatic plant beds in natural system that lack algae and are also covered within the same system. Seasons play a large role in this.