Do the association documents indicate who makes decisions about docking, etc? In my experience there is typically a governing body that dictates where a dock can be put in, how many docks can be put in, how long the dock can be, and so forth. If it is not your local association, it could be your local government, or it may be that your state has a department dedicated to protecting and governing natural resources. Look to these rules to give guidance.
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The law with regard to water access and what can be done off shore is incredibly complex and often specific to the particular body of water. It sounds like the water body in question, if totally owned by the lake association, is privately owned, and possibly not subject to state "use" regulation. If there is a governing body of the lake association, that might be the first place to go, but it would require a lot of homework to fully understand what's the situation with regard to your lake. It sounds like you talked with your neighbor and got no where. If the lake association has never dealt with this issue before, would they, or someone else help mediate a resolution? Even if you're right, litigation would be very expensive. You need to talk to a lawyer familiar with water law. My practice is statewide. If you're interested give me a call.