- Video report by ITV News correspondent Stacey Foster
While securing the damaged Toddbrook Reservoir dam in Whaley Bridge, emergency services are trying to work out why it has become so unstable.
People living in Whaley Bridge have never seen or experienced the Dam overflowing with water as the reservoir was too full to cope earlier this week.
ITV News spoke to civil engineer Malcolm Hollings, who lives in the town, and said the "spillway section of the dam has failed".
Ten pumps are being used to pull water out of the reservoir to ease pressure on the dam, with the water level being lowered by half a metre, but what could have caused this to happen?
- What is the dam wall made out of?
The dam wall is made up of clay and soil covered with slabs which make up the spillway.
The spillway is designed to take on excess water from the 286 million gallons of water which pump through the reservoir.
The slabs have broken off from the wall possibly because of the heavy rain from a few days ago.
- Why are people concerned about the spillway?
The clay and soil has been left exposed as the slabs are no longer there which means water could potentially be let through - and eventually create a hole - leaving millions of gallons of water to flow at speed into the nearby town.
- Is this the first leak from the Toddbrook Dam?
The dam has had leaks in the past in the 1960s and 1970s but today the entire structure is at risk.
Canal & River Trust's Julie Sharman told ITV News: "There are a lot of dams, for water, for canals, for other usage but it's very, very rare that they fail."
But Mr Hollings said he doubts very much why anyone would build a dam like this now.
"The Victorian dams were built in this manner, a more expensive form would have been to build a gravity dam using stones and brick," he added.
- How do residents get alerted of an emergency?
Emergency Services will be notified by radio of a breach to the dam, at that point the nearest person to the klaxon will wind the horn to send an alert across the whole valley.
The investigation to establish what has happened will take weeks and repairing the damage will take a lot longer.