Rising water.

Flathead Lake is a large natural freshwater lake--with a 10 foot deep resevoir on top of it! Kerr Dam is located on the Flathead River four miles downstream from the lake. The dam is over 200' high, but it only regulates 10' of lake level. Since 1939 the dam has been used to maintain a constant lake level through the summer months (known locally as "full pool") followed by an 8 to 10 foot drawdown through the winter months.

As a result most docks are spared from the ravages of winter storms--during the worst winter months they sit high and dry. It also makes dock maintenance a snap, provided that you can get the work done in early spring.
When I made my first (pre-sabbatical) trip to the lake at the end of April the level was at 2885' elevation, or about 8' below full pool (defined by local custom and agreement as 2893' above mean sea level). By the time I got back, just before Memorial Day, the level was up 2 feet and rising fast. The water managers had closed the flood gates at Kerr Dam and the water was rising noticibly: from May 20 to June 6 the level rose over 6' (about 4" per day). This is quite amazing when you consider that the lake covers more than 120,000 acres.

To illustrate this rapid rise, on the morning of May 29 I took a picture of our boat lift--water was just about to reach the bottom rail. I always like to be at the lake when this happens--it tells me if the boat lift needs any adjustment for level. The next day I took another picture, at this point the bottom rail was completely underwater.

Today the level was about 4" below full pool--plenty deep enough for diving off the dock or putting the boat in the water.

Data on Flathead lake levels are available from the USGS.