The so called "hole in a lake" is actually a spillway for automatically controlling the maximum level of a lake, created by a dam. Unlike other spillways these spillways are surrounded on all sides by water and from top these look like a hole in water surface. Such spillways are also known as morning glory hole or glory hole or plughole or inverted bell-mouth spillway.
Jatiluhur Reservoir, Java Island, Indonesia (Mouth diameter 90 metres - 295 feet)
Whiskeytown Lake, Shasta County, USA (26.8 metres - 44 feet)
Ladybower Reservoir, Upper Derwent Valley, Derbyshire, England. (Two numbers - 24.3 metres - 80 ft each).
Berryessa Lake, Monticello Dam, California, USA (22 metres - 72 feet).
The cylindrical shaped tower is multi-purpose and besides being a spillway it also acts as intake for water turbines and Irrigation channel located underneath the tower.
Source of info and more info: jatiluhurdam.wordpress.com (In Indonesian) (English Translation)
The spillway crest has a diameter of 26.8 metres (44 feet) and the bore gradually tapers down to 7.5 metres (24.5 feet).
Image from Flickr is by pressuretobear
Image Source Google Maps
View location in Google Earth / Google Maps
Main source of info: US Bureau of Reclamation (pdf)
Credits: I am thankful to Maria Kokokovitch for bringing this to my knowledge.
The Ladybower Reservoir has been provided with two bellmouth overflows (locally named the 'plugholes') each having inlet diameter of about 24.3 metres (80 ft) which tapers to about 4.5 metres (15 ft) at its exit located at the base of the dam.
View location in Google Earth Google Maps
Source of Info: Wikipedia
Credits: I am thankful to Anonymous for bringing this to my knowledge.
Image from Panoramio is by Auggee
This is how it looks when water level is down;