A group of 'super' foxes was shot dead in Danson Park after burrowing into the banks of the lake, risking "serious" flooding to 80 homes.
B & D Pest Control disposed of 14 foxes which had dug deep holes into Danson Dam, having been called out by Bexley Council because it was an emergency.
Worried neighbours could hear the shots from afar and have labelled the act "inhumane" and "sickening".
David Chamberlain, 54, of Danson Lane, said: "The traps were very loud, imagine a gate clanging, that is how loud it was and I heard it twice from my house.
"I was quite shocked because the park is full of wildlife
"The park is a nature reserve and you expect there to be wildlife.
"I think it's inhumane and sickening."
Urban wildlife consultant John Bryant is working with Bexley Council on what to do in the future for the area after the incident on June 16.
He said: "I went up to Danson Park years ago and they had the same problem.
"Shooting the foxes is pointless because within three days new ones will move in.
"The burrowing into the embankment will weaken it and the foxes will keep digging if they can.
"The bank needs to be dealt with it and that is what I will be looking at with the council."
A spokesman for Bexley Pest Control said: “ I have worked in pest control for more than 20 years and never heard of foxes burrowing that deep, they would have to be super foxes to do that.
“They normally burrow under garden sheds, I have never heard of them causing structural damage.
"It is illegal to move foxes from one area to another, they have to be disposed of."
A Department for Environment, Food & Rural Affairs policy statement in 2010 said: "Previous attempts to kill urban foxes to achieve a sustained population reduction have not been successful in the long-term because of the mobility of foxes and their ability to produce offspring in large numbers; territories made vacant by culling resident foxes are rapidly colonised by new individuals.
"The most effective strategies to resolve fox problems have primarily relied on non-lethal methods, focusing on preventative and deterrent strategies."
A Bexley Council spokesman said: "During one of the regular inspections of the dam it was revealed that foxes had burrowed deep into the clay and soil that make up the embankment behind the dam.
"The damage was enough to cause serious concern.
"Should the dam break, up to 80 houses downstream would be at serious risk of flooding, major disruption would occur.
"Danson Road would be closed to traffic and the lake itself, a valuable habitat for wildlife, would suffer catastrophic damage.
"This was an unusual situation and had not occurred before at the park.
"B & D Pest Control carried out the operation using approved methods.
"They are licensed to use firearms with considerable experience in this kind of pest control.
"The company informed Bexleyheath police who raised no objections and the foxes were humanely destroyed on the night of the operation using firearms.
"‘Our engineers are now in discussion with a wildlife specialist to find a longer term solution that will discourage future attention from foxes."
Bexley Police said they were aware of the incident.