Actually, I think it's a very good question. Ellsworth and the Hancock County Soil and Water Conservation District have helped private roads along City lakes (Branch, Green, Patten Pond) used EPA 319 B grant money for improvements to prevent runoff etc .The  City also had grants for property owners to improve ldriveways and lake front properties to prevent runoff. When I googled it I found this: https://www.federalregister.gov/documents/2003/10/23/03-26755/nonpoint-source-program-and-grants-guidelines-for-states-and-territories  Not sure if this link will work but you can google it. There may be more grant type money out there. You could check with your town, soil and water district, and similar agencies. These grants were all matching, up to 50% of project costs, I believe. Good luck.  

Note: It may qualify for runoff into the lake even if it is some distance away.  As long as it is in the watershed, runoff from the road will eventually make its way down to the lake.  My daughter's road association (that I mentioned above) got a grant to have two culverts replaced because they were in danger of washing out when there was an intense rain storm, and that would have dumped road materials into a stream that ended up in the at-risk lake.