While sewage and fertilizer runoff need to be managed, those are not even remotely close in scale or impact, and they also pale in comparison to the acidification of our oceans due to uptake of CO2 from the atmosphere.
https://en.m.wikipedia.org/wiki/Ocean_acidification
I disagree. This problem is too big for minor actions from tiny handfuls or conscientious people to matter.
Sure, you using fewer squares of toilet paper each time you poop and ceasing use of plastic straws is nice, but you’re basically putting bandaids on compound fractures and ruptured organs.
We instead need system-wide / planet-wide legislation to convert our sources of power, its distribution, and the way it gets used. We also need to invest heavily in carbon capture, green infrastructure, and agriculture to account for coming droughts, floods, and ferocious storms. We need to be moving people away from coastlines, reinventing air travel, and ending use of coal, petroleum, and more.
We need to shift the entire paradigm, not just tweak the margins. Nothing less will rise to the actual challenge before us.