What does it mean when it says same dna in all tissues?

Good afternoon, Lycasey16. Thermal pollution is a real thing because whenever we heat water, the dissolved oxygen decreases. Dissolved oxygen is how you can tell how healthy the water is for the aquatic animals. Too little dissolved oxygen will result in death of many organisms. Same thing with thermal (water) pollution. If you heat the water too much, dissolved oxygen will decrease which will kill many marine life. Thermal pollution is one of many that causes the water to become polluted. I hope this helps, have a great day.