There are varying models on the origins of the flood waters. As with many theories, there are strengths and weaknesses. This link explains the different flood models. Some creationists believe in the Canopy Theory, where a canopy of water surrounded the earth prior to the flood. During the flood, that water fell down as rain. Another possibility is the Hydroplate Model. The following the animation video below provided by Dr. Walt Brown of www.creationscience.com explains the Hydroplate Model.
In Genesis 6, we read where God commands Noah to take two of every kind of land-dwelling animal on the ark. This includes the mammals, birds, and reptiles, but not the fish. There is some debate if insects were included. During the flood, the salty ocean waters would have mixed with the fresh lakes and rivers. How did the fish in the fresh waters survive in the salty mixture? How did the saltwater fish survive in the fresh mixture?
There are many areas in the world where freshwater and saltwater are together, but the waters don’t mix. Studies on water have shown that various temperatures, chemistries, and sediments in the waters don’t mix but instead become segregated. It is possible that the fish survived in “pockets” of fresh or salt water, depending on the species. Before the flood, the fish would not have been affected as strongly by the curse like they are today, so they may have been able to tolerate the water mixes during the flood and adapt to the different chemical makeups. It should be noted that the majority of fossils are marine creatures, so most fish died during the flood when they were buried by sediments. We know that two of each kind of fish survived, though, because we see them and their variations swimming in bodies of water today.
For further reading on this often asked question, see the two following articles:
The following information comes from “Your Guide to the Grand Canyon” by Tom Vail.
Many people are taught that the Grand Canyon was carved out by the Colorado River that runs through it. Could a river create such a large canyon? Uniformitarianism scientists agree so. But how could this have been formed in light of Noah’s Flood? Recall the article “Where did the flood waters go?” Was it formed by a little bit of water over a long period of time, or a lot of water over a short length of time? There are two theories that explain how the Grand Canyon was formed relatively quickly:
Theory 1: After the flood, there were two or three very large lakes that formed north and east of the Kaibab Plateau (through which the canyon is carved). As the lakes continued to fill, they finally overflowed and breached their natural dams, carving through the loose sediments in the Plateau, and thus creating the canyon.
Theory 2: There was massive sheet erosion during the flood’s recession (after the 150 days of water covering the earth). As the waters receded off of the land, they channelized as more land was exposed. It was during this process that the waters moved westward and carved through the loose sediments, creating the canyon.
More information about the Grand Canyon can be found at: http://www.answersingenesis.org/articles/cfl/grand-canyon
Watch the following video to witness the awesome power of water. But first, click on this link to understand more about the video. This sheds light on how the Grand Canyon could have been formed.
The canopy theory offers an explanation for what happened on the second day of creation and also provides a source for where all the water came from during Noah’s Flood. The model states that when God separated the “waters from the waters” (Gen. 1:6) on Day 2, he left water on the Earth in the oceans and the rest went up into the atmosphere, forming a protective water canopy that encircled the Earth. This would prevent short wave radiation from entering the Earth. Radiation is known to cause harmful effects to our bodies, so people on Earth were protected and lived long, healthy lives. When the flood started, the canopy fell down as rain, covering the earth and killing everything that was not on board the ark.
There are problems with this model, one being that it would create a greenhouse effect that would make the Earth so hot that people could not live on it. Some creationists still hold to this model while others have moved on to other theories and formulated new ideas.
One thing to keep in mind as we formulate ideas on the pre-flood world is this: we don’t know what the world was like then. We can’t say with certainty that all systems we have today were in existence prior to Noah’s flood. The earth back then could have been profoundly different. Some questions may never be answered on this side of heaven.
More information about the Canopy Theory and some of its problems can be found here.