All the earth's oceans have varying contents of bacteria, plankton, and land runoff. What the area was like at the time you were there I don't know, but suffice it to say that all water sports participants should take hygienic precautions before, during, and after participation. Don't drink the water, don't go if you have an open wound, afterwards clean any cuts and scrapes with warm soapy water and a diluted hydrogen peroxide preparation. I often tell my patients who are susceptible to sinus problems to learn how to empty their sinuses by bending over forward and tilting the head side to side to get the major sinuses to drain. This is due to the fact that the major sinus openings are towards the top of the head and inversion allows some gravitational drainage.
Gentle nose blowing helps complete the task.