How I have to model and what material and composting to use to achieve this look of the lake underwater weeds on the very beginning of a video and on 1.20 as well, that small slimeish weeds called " Spirogyra", even know the name after searching in Google 
I suppose I have to blurry them in compositor, maybe? And what model to use low poly or high poly? It’s gonna be animation with a lot of animated plants, so bear in mind, please.
For the Mist check this out: https://www.youtube.com/watch?v=CxNeMMZs_sM
If that’s not enough you should have a look at volumetrics but this will totally kill your render time and is probably not needed.
For the modelling you should play around with Hair (and Hair physics for animation) that should bring you pretty close. While searching for this you should also have a look at the materials used there, copy the concept and maybe add a little emission. The slight emissive look might just be the very low contrast in the video.
Here’s a very fast mockup to show you the base concept I’d use. Needs a lot of fine tuning everywhere but that’s the fun about it, right? Download the blend to see the animation. (Mist not included here)
seaweed.blend (4.04 MB)
Thank you for this. Didn’t have time to check it yet, but will as soon as I will come near my computer. Yea, probably you right it’s better to use hairs than models for such a slimeish thin plant
Played with that. Made a few changes and i think thats quite close that i was looking for, though this is a bit different weed now, called algae (tangles in the roots of a trees), but from the same slimeish type. Dont know though if will be able to render this, especially animation,since even such a still image already killing my expensive laptop with dual 1070. Will have to play with the settings maybe and to switch off some hair rendering settings maybe
