Complex sentence: While swimming in Sun Moon Lake is usually not permitted, there is an annual 3-km race called the Swimming Carnival of Sun Moon Lake held around the Mid-Autumn Festival each year, and in recent years the participants have numbered in the tens of thousands.
Split into simpler sentences: While swimming in Sun Moon Lake is usually not permitted, there is an annual 3-km race called the Swimming Carnival of Sun Moon Lake held around the Mid-Autumn Festival each year. In recent years the participants have numbered in the tens of thousands.