Question

how can pathogens like coliform enter freshwater systems?
through excess nutrients getting into the water.
through over application of pesticides.
through erosion of topsoil
through leaky septic tanks and dog poop.
rewatch

Explanation:

Coliform bacteria are typically associated with fecal matter. Leaky septic tanks release human waste containing coliform, and dog poop is a direct source of fecal pathogens. Excess nutrients cause eutrophication, pesticides introduce chemicals, and topsoil erosion moves sediment—none directly introduce coliform pathogens like fecal sources do.

Answer:

Through leaky septic tanks and dog poop.