Usually yes at monitored swim areas - but natural water is not pool water: the CDC's first rule is check before you go (advisories and closures), especially after heavy rain, which washes fecal contamination into swim areas for days.
The main risks: gut germs from swallowing water, harmful algae blooms (scum or paint-like surface = stay out), and swimmer's itch in snail-heavy shallows. Never swallow the water, stay out with open cuts, and the physical rules outrank everything: cold shock, currents, drop-offs, no lifeguard. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper .
What to do
Common questions
Is it safe to swim in lakes?
Usually yes - at designated, monitored swim areas, lake swimming is a normal, low-risk pleasure - but natural water is not pool water, and the safety rules are different. The CDC's natural-water guidance sets the hierarchy: first, check before you go - look up whether the swim area is monitored, under advisory, or closed, especially after heavy rain, which washes animal and human waste into swim areas and spikes germ levels for days. The main risks, in order: waterborne germs (gut bugs from fecal contamination - the swallowing-water route, mostly), harmful algae blooms (blue-green scum or paint-like surface = stay out entirely, pets especially), and swimmer's itch parasites in snail-heavy shallows. The habits that cover them: never swallow the water, stay out with open cuts or wounds, skip creeks and unmonitored spots, rinse off after, and keep ears dry-ish if you are prone to swimmer's ear. Special caution: anyone immunocompromised should check with their clinician before natural-water swimming. And the physical rules of open water still apply and outrank everything above: cold shock, currents, drop-offs, and no lifeguard - swim parallel to shore, use a bright buoy, and never alone.