Your turtle does need a filter for a few reasons. Any aquatic animal needs to have a filter, and even though turtles are relatively sturdy, they still need a clean environment to live in. Turtles produce a lot more waste than fish do. Therefore, their tank gets dirtier faster. A proper filter will take care of that through the different stages of filtration. A filter will also circulate the water and make sure there’s a fair amount of oxygen within the tank.
If the turtle’s tank gets too dirty, then it can make the turtle sick. On the other hand, there will be a strong odor that will bother the turtle, but it will bother you as well when you’re in the same room as the tank. Aquatic turtles need to have plenty of space to swim, but they also need to bask too. The entire tank will not be filled with water, but that doesn’t mean the tank will be easier to clean. Therefore a filter is not needed. To make your life easier and give your turtle a clean, healthy environment, a filter is necessary.