My first thought about this was “snow on a mountain”.
Then, “waterfall”.
Then, “spring run-off”.
Some people have mentioned “water towers”.
Could be just about any form of H20: ice, rain, pond, or steaming, erupting geyser.
This bridge is about twenty feet above the current water level.
I was in Iowa City five years ago for the big flood. They told us not to worry that week, while they secretly emptied the art gallery, and we watched the Army Corps of Engineers sandbag the railroad line.
Don’t alarm the (paying) public….
The Fenn Diagrams 
I dont know how old this is considering there is no date, but my wife was talking to me about Fenn’s Treasure last night so I read it. Now, thanks to her, I think I’m hooked….
Could it be possible that “Just heavy loads and water high” is talking about a bridge above a water crossing? Heavy Loads would mean a strong bridge since many smaller ones have signs that say “no heavy loads” and “water high” means a high stage of water in a river of lake; high tide. Those together make the thought complete: a bridge.
Definitely! The question would be, which one?
High Lake