That link that Flingwing pointed to has this sub-page, which is my guess as to what was happening:
"Microbial activity tends to concentrate at the gasoline-water interface. Moderate activity may cause the gasoline to lose brightness and clarity. Severe activity may stabilize gasoline-water emulsions and contaminate the fuel with visible particles of microbial sludge (biomass). Anaerobic microbial activity may generate hydrogen sulfide, giving the gasoline a "rotten egg" odor."
Moisture is present in every temperature change, where the tank vents breath in moist air, and cool conditions can condense it. The quote says "emulsion" as in a colloidal suspension of water and gas. The sunlight could have made some tiny airborne algae particles happy guys for a while. Modern anti-polution fuels get biological growth more easily, and biocides are recommended.
If it is suspended water with biological contamination (could there be a simple test for it?) the fuel is gone. Good for bonfires and the like.