how do I render my animation and the rest of the scene seperately I have a scene that scatters over a million grass plants on a landscape and also an animated river that runs through the landscape. As the river is the only thing hats animated is there any way I can render the landscape and grass once instead of over and over each frame along with the water?
You can render the first static frame, save it as image and then plug into Alpha Over node in compositing.

Disable animated river. Uncheck Disable in Renders icon in the Outliner tab: 
Render only Statics and save on disk: 
Enable the river in Render and disable all statics (same as 1)
Check Fill&gt;Transparent (available for both Eevee and Cycles):
Set up compositing Alpha Over node:
Render the river. Compositing will be executed for each frame of the animation: