(CNN) Preliminary data indicates that US Border Patrol arrested around 51,000 people on the US-Mexico border in August, according to a Border Patrol source familiar with the data.

The August numbers show a consistent decline in arrests since the spring and come as the Trump administration has pushed forward numerous controversial policies intended to help stem the flow of migrants arriving at the southern border. An influx of migrant families and children, predominantly from Central America, strained resources along the border as severe overcrowding took hold earlier this summer.

Border Patrol apprehensions, a measure of illegal crossings, dropped around 30% from 71,999 in July to around 51,000 in August, according to the preliminary data.

Homeland Security acting Secretary Kevin McAleenan on Wednesday, appearing alongside President Donald Trump in the White House, said that preliminary border statistics indicate "a reduction of over 50% from May to today." The statistics will be released early next week.

The August numbers mark a significant decrease since the high in May of more than 130,000 arrests, but it still remains higher than any month in the past two fiscal years. Many migrants arriving at the southern border turn themselves into Border Patrol after arriving on US soil.

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