To calculate the volume of the lagoon, we need to find the volume of each section and then subtract the volume of the rectangular top.
The volume of a rectangular prism is found by multiplying the length, width, and height. So the volume of the rectangular top is 50 ft * 20 ft * 0 ft = 0 ft^3.
Now let's find the volume of the triangular sides. The volume of a triangular prism is found by multiplying the area of the base by the height. The base area of each triangular side is (1/2) * 50 ft * 20 ft = 500 ft^2. The height of each triangular side is 25 ft.
So the volume of each triangular side is 500 ft^2 * 25 ft = 12500 ft^3.
Since there are four triangular sides, the total volume of the triangular sides is 4 * 12500 ft^3 = 50000 ft^3.
To find the total volume of the lagoon, we need to add the volume of the rectangular top and the volume of the triangular sides. So the total volume is 0 ft^3 + 50000 ft^3 = 50000 ft^3.
Therefore, the lagoon can hold 50000 ft^3 of water.