From my understanding off road diesel is ethanol free, whereas (vehicle) gas stations may be selling you e- diesel, with as much as 15% ethanol. Marine stations "supposedly" sell only ethanol free diesel.
E diesel is a blend of standard No. 2 diesel fuel containing up to 15% ethanol and a proprietary additive to maintain blend stability and certain fuel properties, which may comprise from 0.2% to 5.0% of the blend. Currently, E diesel fuels are considered experimental and can be used legally in off-road applications. Special permission must be obtained from the U.S. Environmental Protection Agency (EPA) for on-road use.