The answer is that the lake level would have been pretty much the same as it is today, as long as you were visiting the lake in the spring. As the summer wore on it would have dropped considerably, especially in dry years.
In 1920 the water users of Payette Valley got together to apply for a storage water right on the lake of 50,000 acre feet of water. The previous year had been a dry one, causing a shortage of irrigation water in the lower Payette valley. It was the first time that had happened. Irrigators wanted it to be the last.
The Lardo Dam was born. The 120-foot dam was built to a height of about 8 feet. That cost about $20,000, a fair piece of change in 1920. Its function was to hold the lake at or near its ordinary high water mark most of the season so that it could be drawn down as needed.
Things went along well for the Lardo Dam until August of 1943 when it washed out, dropping the lake level two feet in a single day. It was replaced later that year and is still in operation, keeping the lake high for boaters, swimmers and, not incidentally, irrigators.
One interesting side note about the dam was the article written about it in the Caldwell Tribune, on March 5, 1920. The lede paragraph said, in part, “According to the application filed with the state commissioner or something or other of the Governor’s cabinet…”
The commissioner or something or other? I suspect the writer plugged that in, meaning to find out the name of the something or other before publishing the article. Then they forgot, giving me the chance to make fun of them a hundred years later.