Why did the Indus Valley Civilisation stop

The Indus Valley Civilisation grew steadily and prospered for about 1000 years. Around 1500 BCE, the Indus Valley Civilisation rapidly declined. It ended with Mohenjo-Daro being abandoned around 1200BCE and Harappa soon after. Archaeological evidence, such as signs of constant rebuilding of walls and foundation of houses, suggests that floods could have caused the decline of the Indus Valley Civilisation. These woluld also have destroyed the irrigation systems that the people depended on for their farming. Some scholars think that the floods might have bred mosquitoes which led to outbreaks of malaria. Whatever the reason, the decline was almost certainly speeded up by the invasion of the Indus Valley by a group of people called the Aryans(Adapted from The Living Past History Of Ancient India,China and Southeastasia 2nd edition)