Pea soup colored pond water occurs when a pond lacks good bacteria. In the formal pond above, the water is green because the pond is relatively new and has not had the time to establish healthy colonies of bacteria. The pond is also bare-bottom (no gravel at the bottom) which reduces the surface area for bacteria to colonize.
An easy way to remedy this problem is to do a simple water change. Since this Bethesda pond has a built-in overflow, a pump is not needed to drain the green water. Adding new water from the garden hose until the water clears is the easiest solution to the problem.