The pipeline company has argued that the risks to the water supply are minimal and that the tribes didn't raise religious concerns earlier in the approval process.
Standing Rock Sioux and Cheyenne River Sioux tribes claimed the project will prevent them from practicing religious ceremonies at Oahe Lake which they say is surrounded by sacred ground.
In prepared testimony overnight for a hearing before a House energy subcommittee, Mr Mahmoud also blasted the Obama administration, which twice delayed the project a year ago.
Judge James Boasberg denied a request to block construction on the last stretch of the Dakota Access Pipeline.
In his testimony, Mahmoud also said the pipeline, which will carry shale oil from North Dakota's Bakken Region to Patoka, Illinois, has been "subjected to a series of politically motivated actions by the previous administration, accompanied by a host of half-truths and misrepresentations in both social and mainstream media".
Twitter Temporarily Limiting Reach Of User Accounts Sending Abusive Tweets
What this essentially means is that people outside the offender's network of followers will not be able to see their tweets. Or, if someone retweets a tweet from a punished account, the retweet won't show up to users not following the account.
The Standing Rock Sioux began coordinating a cleanup in late January.
A US federal judge denied a request that would have stopped work on the final final 1,100 feet of the pipeline.
Energy Transfer Partners, the company bankrolling the project, said they have about 60 days of construction left until the pipeline is done.
Although this is a setback for the Indigenous water protectors fighting the pipeline, the judge did say he would consider the case more thoroughly on February 27.
Abandoned property used by people who temporarily occupied the Oceti Sakowin camp to protest the Dakota Access pipeline is piled in front of Dumpsters headed to the landfill.
The impact of Kevin Love's knee injury
Korver ended Indiana's chances of winning the game, hitting a pair of threes to break an 83-83 tie early in the fourth. For, I remember two years ago, when Love was injured in the playoffs, causing him to miss the Finals.
Numerous activists who have been protesting in North Dakota have vowed to stay, although the primary protest camp is on a flood plain on Army Corps land and is being cleared.
Up to 400 people continue to occupy the main anti-Dakota Access protest camp near the Standing Rock reservation on the Cannonball River floodplain.
Mr Mahmoud challenged the tribe's objections and said the pipeline poses little threat to drinking water.
The irony of the anti-pipeline movement's "water protectors" leaving behind a fossil-fuel mess isn't lost on local officials like Rob Keller, spokesman for the Morton County Sheriff's Department.
Court to Rehear Case on CFPB's Constitutionality
The CFPB says that over five years it has recovered $11.7 billion that it returned to more than 27 million harmed consumers. The case is being closely watched because it could determine the fate of CFPB Director Richard Cordray.