Which of the following is true about the modification of a boat's muffler system?

The statement that modification of a boat's muffler system is prohibited if it increases noise levels is accurate because regulations are designed to minimize noise pollution and protect the natural environment, as well as to ensure the comfort of other boaters and nearby residents. Excessive noise can be a disturbance on waterways, leading to restrictions that aim to maintain tranquility and safety.

Many boating regulations, including those in Missouri, specifically address the requirement that boats must adhere to certain noise limits. If modifications to a muffler lead to noise levels that exceed these limits, such alterations would be considered illegal and subject to fines or penalties. Therefore, this regulation emphasizes the responsibility of boaters to comply with laws intended to maintain a peaceful and enjoyable boating experience for everyone.

The other options suggest allowances for modifications under certain conditions, but they don't align with the emphasis on maintaining noise control through regulation. Thus, the key focus is on preventing modifications that result in increased noise levels while clarifying that not all modifications are inherently permitted or allowed based solely on noise reduction.