The person is called a Marshal.
To swim 300 yards it would be 12 lengths of the pool. Although there are no 300 yard races in competition swimming. It goes from 200 yards right to 500 yards.
It is debatable about what an average person is. An average swimmer can swim 2640 yards in about 30-50 minutes. It just depends if they are a swimmer.
people can swim for a long time. there is miles, yards, there are for hours at a time. The longest that i have know is that of going on for 7 hours in that time the person swam for 40600 yards. Yet this was only a study of how long a person could swim at a constant rate.
You only have to swim 1,760 yards to equal one mile.
750 meters = 820.209974 yards
Most people (that can swim) can swim 400 yards. The speed of how they do that although varies.
0.5 mile = 880 yards - whether you swim or walk or run is irrelevant.
It is when you swim competitively. You take part in races. You swim to go fast.
No:400 meters is the same as 437.45 yards500 yards is the same as 457.2 meters.