According to your headline and the wording of the question Iassumethat the base area of the pool has to be an ellipse.

1. Area of an ellipse:

...... Sub in the values for a and b (in meters!)

...... therefore the volume of the pool is:

Use the property: One liter is the same as one decimeter cubed and one decimeter is the same as 10 cm. Therefore:

So the pool contains:

to the nearest 10 l.