My first question is, What is the utility of your lake? The definition of a lake is a large body of water surrounded by land, and the definition of a pond is a body of water surrounded by land, smaller than a lake. So a lake is a large pond, while a pond is a small lake. Large and small are subjective assessments. Value difference in my markets often come down to utility. Can you ski on your lake? Are motor boats allowed? The more activities one can do on a given lake compared to any other lake makes a large part of the value difference. In my area, if I compare a ski-lake to an "electric motor boat only" lake, I'd have to seek out the market reaction difference. A large lake in my area that is limited to only fishing, can be equal to a pond where there are fish, and very inferior to a smaller lake where skiing is allowed.
My other point, though, is, there are two ways to tackle an appraisal problem. An appraiser can pick the three most similar sales in the market, or the appraiser can select the three most similar sales that bracket the subject's overall appeal in the market. This can lead, rightfully, to the use of different comparables from one appraiser to another. The latter method is known as "the bracketing method" and is what FHA requires.
Generally, in bracketing, the appraiser determines a probable range of value for a property, using qualitative techniques to a pool of sales. This pool is divided into two groups: Those superior to the subject, and those inferior. To bracket the subject's appeal, one from each group must be selected, and the third can would be the most similar sale to the subject regardless of which group it is a part of. It could be that your appraiser believed the 5 acre sale with a pond to be the most similar and best indicator from the inferior pool of sales. It is a judgement call. But my opinion is simply if one of the comparables in the report is superior to your house, and one is inferior, and both are market sales, then the appraiser more than likely set up the logic puzzle in a sufficient manner, and the value is going to be within a reasonable, acceptable range - often even if larger mistakes are made.