Don't know where the lake property is or how large, or codes, etc. - but Wally would dig a "gopher hole" for the black water (holding the contents till nearly full and then dumping periodically) and water some trees and shrubs with the gray...
We occasionally dump our black water into a "gopher hole" we dug and covered with a piece of plywood with a hole cut into it. When the whole fam comes to visit, we give them the house, and we retreat to the Minuet for the evening. After they leave - we dump - no problems with odors - it's on the wooded part of our 3/4 acre residential lot.
The trees and english ivy seem to appreciate it...