Before and after the valves were opened on Monday.
Last week, the Mercury reported on how the dam is leaking – potentially jeopardising lives as well as property, roads, railways and the Midlands' canal network.
Engineers have recommended that 'urgent and extensive' work on the problem starts at once and on Monday the valves were opened.
"Opening the valves to drain the reservoir signifies the start of a major programme of safety improvements," said Councillor Val Richards, Lichfield District Council's cabinet member for leisure services.
"Getting to this stage is the culmination of a lot of hard work, and it is good to finally get started on these works as it is essential that we make sure the dam meets current safety standards, making it safe for years to come."
The reservoir, at Chasewater Country Park, is one of the largest in the West Midlands.
Although the council does not own or control the water, it is responsible for it and the dams under the 1975 Reservoirs Act.
Now the valves are open, water is beginning to flow into the Anglesey Branch Canal and then into Crane Brook – which will join the River Tame, in Fazeley.
Visitors to Chasewater will notice the water level drop dramatically over the coming months, exposing the muddy reservoir bed.
Temporary information panels warn visitors to keep off the bed due to the dangers of soft, deep mud and silt.
While the work takes place, people should:
● Stay on marked footpaths;
● Keep children and dogs under close supervision, away from the reservoir bed;
● Not walk on the exposed reservoir bed at any time.
"It is very important that visitors follow our safety advice," added Mrs Richards.
"However, I would like to stress that Chasewater Country Park will be open as usual. Visitors can still enjoy the surrounding countryside and facilities, including the heritage railway and Innovation Centre."
Water is seeping through the main 560-metre long eastern dam.
Experts have warned that if it were to fail 'quickly and catastrophically', up to 80 people could die and the homes of more than 2,000 others would be affected.
With warnings of a potential wave of water up to five metres high and a kilometre wide, rushing downstream at 12mph, a sudden flood could swamp nearby settlements causing more than £100m in damage.
The council has already invested over £750,000 to determine what must be done, although it cannot begin until the water level has been lowered.
After that step, remedial work should take around seven months.
The council expects to start refilling the reservoir in September.
However, it could take between two and four years to get back to normal, depending on rainfall and the amount of water needed by local canals.
"I would like to extend our gratitude to the clubs that use Chasewater Reservoir for their understanding and patience," added Mrs Richards.