@gembo I too saw the BBC article the other week about Legionnella from compost. Was slightly confused as it said it was transmitted probably from disturbing the compost and breathing in droplets, then recommended hand washing!
Apparently Legionella will and do live naturally in open water sources (e.g. ponds lakes reservoirs) although it is both below their ideal temperature for multiplying and requires the water to be disturbed and turned to droplets to form a hazard.