If you're only using moonlight, i would go with maybe 5 minutes to start off on... even in full moon... i expect this means no 'city lights' or 'light pollution'... while shorter exposures work for the above examples, one must keep in mind, that these us artificial light, which are many times brighter than natural light at night (for the most part)

If you are trying to capture fireflies, i would also do as suggested above, but again as a start a 5 minute exposure if not 10 minutes. I would use acros, as they say it has low reciprocity failure, but you have to experiment, as i have found, that with just after sunset, and very little artificial light, and just a the last bit of 'sunset glow' i end up doing about 2 minute exposures, or up to 4 (of course these are very specific for my case)...

Also, i would experiment before i go, especially if it's going to be a trip...

keep in mind, that a full moon might give extra contrast, but would light up the lake seen plenty nice, i think.