The answer could be really ...

The answer could be really long if we go on describing all pollutants and their sources. However, they are either natural or man-made and sources could be anywhere from effluent, domestic sewage, etc. to oil spill in the open ocean. Some of the notorious man-made organic pollutants (like TBT, PCBs, PHC, PAH, etc) enter water environments due to uncontrolled usage and improper disposal. Most of the heavy metal pollutants come from industrial effluents, untreated sewage, river runoff, areal dispersion, etc. This is really difficult to name all the pollutants and their origin at one place. Equally difficult is commenting on the effects of organic effluents on receiving water. Because the nature of the effluent will decide what kind of organic pollutants are there in it. For e.g. effluent from sugar industry or oil refinery will never contain similar organic pollutants. In short, the effect can be very diverse and different. This could be anywhere from making the water body anoxic (in case of oil-containing effluent) to complete fouling (effluent from tannery for example) of the water body.