Which characteristic best explains why algae blooms are more likely to grow out of control in lakes instead of rivers?

Which characteristic best explains why algae blooms are more likely to grow out of control in lakes instead of rivers?
More photosynthetic organisms are found in lakes than in rivers.
Lakes have lower nutrient and dissolved oxygen levels than rivers.
Rivers have higher turbidity, which is preferred by photosynthetic organisms.
Lakes consist of still water where photosynthetic organisms can grow undisturbed.