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You should not expect a garden pool to have the sterile clarity of a swimming pool, but on the other hand, you don't want green soupy water.
Algae is the main problem. The bright sun that helps the water plants thrive will contribute to algae bloom and heating of the water. Overheating of the water can be a concern if you add fish. Plan on extra maintenance if you locate your pond by a tree because of falling leaves, etc. that may blow into the pool.