After months of speculation about when the construction of the U.S.-Mexico border wall proposed by President Donald Trump will start, Homeland Security Secretary John Kelly told Fox News Thursday that it will start by the end of summer. The announcement comes a day before the scheduled visit of U.S. Attorney General Jeff Sessions and Kelly to San Diego to observe federal operations at the border with Mexico, reports said.

"Just in the last 60 to 90 days, the movement of illegal immigrants up from Central America through Mexico has dropped off 70 percent," Kelly told Fox News. "We’re at about a 15, 16 year low, and frankly, we haven’t done all that much yet," he added.

Read: Why Is Trump's Mexico Border Wall Being Sued? 

Although there has been much debate about whether or not Trump's proposed border wall be able to curb the illicit flow of people and drugs, the environmental damage which it will cause cannot be overseen. The existing 654 mile wall and fences on the U.S.-Mexico border has harmed the local ecology already. The wall has cut off, isolated and reduced populations of some of the rarest animals in North America such as the jaguar and ocelot, which is also known as the dwarf jaguar. The wall has led to creation of roads through wild lands and has caused ecological imbalance, according to Vox

The new proposed border wall will threaten 111 endangered species as it passes through four key wildlife reserves on the U.S. side of the border and also several nature reserves on the Mexican side. Several migratory birds such as the bald eagle — America’s national bird — will be affected along with marine animals such as manatees or sea turtles.

Another factor is the emission produced during the construction of border wall. Conservationists pointed out that the amount of concrete needed to build a solid wall across the whole border would produce huge amounts of carbon dioxide with Bloomberg New Energy Finance calculating a figure of up to 1.9 million tons depending on how high it might be.