Holter Lake has two parts, dubbed upper Holter Lake and lower Holter Lake.
The central section of the lake is a narrow, 5-mile (8.0 km) neck, marked at its downstream end by the Gates of the Mountains.
The Gates of the Rocky Mountains were first recorded when the Lewis and Clark Expedition passed through the area in 1805.
Captain Meriwether Lewis wrote on July 19, 1805:
this evening we entered much the most remarkable clifts that we have yet seen.
these clifts rise from the waters edge on either side perpendicularly to the height of 1200 feet. ...
the river appears to have forced its way through this immense body of solid rock for the distance of 5-3/4 Miles ... I called it the gates of the rocky mountains.

The Gates of the Mountains has been tourist attraction since the period 1886 to 1906, when the steamboat Rose of Helena traversed the Missouri River through this area.
Although the Missouri River once ran swiftly through the Gates of the Mountains, Holter Dam drastically reduced the flow of water so that now the area has almost no current.
Water levels in the Gates are now 14 feet (4.3 m) higher than they were in 1805.
Holter Lake has two parts, dubbed upper Holter Lake and lower Holter Lake. The central section of the lake is a narrow, 5-mile (8.0 km) neck, marked at its downstream end by the Gates of the Mountains. The Gates of the Rocky Mountains were first recorded when the Lewis and Clark Expedition passed through the area in 1805. Captain Meriwether Lewis wrote on July 19, 1805:
this evening we entered much the most remarkable clifts that we have yet seen. these clifts rise from the waters edge on either side perpendicularly to the height of 1200 feet. ... the river appears to have forced its way through this immense body of solid rock for the distance of 5-3/4 Miles ... I called it the gates of the rocky mountains.
The Gates of the Mountains has been tourist attraction since the period 1886 to 1906, when the steamboat Rose of Helena traversed the Missouri River through this area. Although the Missouri River once ran swiftly through the Gates of the Mountains, Holter Dam drastically reduced the flow of water so that now the area has almost no current. Water levels in the Gates are now 14 feet (4.3 m) higher than they were in 1805.
Holter Dam