This is most often caused by too many nutrients and too little water flow. It is also contributed to by overuse of fertilizer and destruction of rooted plants along the shore and bottom. When present, these rooted plants use up nutrients and keep algae from growing quickly.
The submerged plaints in canals decompose and float to the surface. It is primarily seen in the late summer and early fall.
Low oxygen and too much organic waste could also be a cause, or it could be anaerobic mud turned by storm events. If this is present after storms, the mud will gradually settle again.
FILM ON WATER
Some is natural and normal, and will dissipate with rainfall or time. Oil and gas could cause this - look near boats, watch for people dumping oil, etc. into storm drains as they lead directly into canal
SLUDGE ON TOP OF WATER
After storms or high winds, this could be algae broken loose from the bottom. It will gradually settle again.
Help us by picking it up with a net and throwing it into your trash or garbage, or call our office.
This could be tannins released from upstream, and should eventually wash out. If the water is cloudy, then it could be a turbidity problem due to dumping or construction work.
In warm weather, this is often caused by a lack of oxygen and the fish suffocate. This could also be due to the introduction of toxins (i.e. pesticides) by runoff or dumping.