For your referecnce, typical chemicals found in petrol:
Toluene
Xylene
Pentane
Trimethylbenzenes
Benzene
Butane
Ethylbenzene
Heptane
Cyclohexane
n-Hexane
n-Octane
Ethanol
Naphthalene
Trimethylbenzene
Isopentane
Styrene
Methyl tert - butyl ether
Ethyl tert - butyl ether
Tertiary - Amyl methyl ether
Alkanes, Cycloalkanes, Alkenes, Aromatic hydrocarbons
Many of these are carconegens. Thats what you are putting through your boat. How much of this ends up in the water is anyones guess. I could not find any references to it. Perhaps a study has never been done. In any case, I would suggest that any by product from burning petrol and oil would be so greatly diluted in the water that it would be immeasurable. Run off from roads alone would create more pollution.