During the flood, Noah's ark was sustained by floating on the water. As the water level rose, the ark was able to remain afloat and not sink because of its size and shape. It was built with a flat bottom and sloping sides which helped it to ride out the waves without tipping over. Additionally, the ark was built using strong, durable materials like gopher wood and was coated in pitch to make it waterproof. This allowed the ark to withstand the heavy rain and flooding for 40 days and 40 nights. So, the correct answer is "floating on the water."