Teich vs. Weiher
While both Teich and Weiher translate to "pond" in English, the difference lies primarily in how the water is regulated and created. A Teich is strictly artificial and manageable, while a Weiher is often natural or lacks a drainage system.
Teich
A2A Teich is an artificial standing body of water created by humans, which typically has an inlet and an outlet to control the water level or drain it completely.
Mein Vater hat im Garten einen kleinen Teich für seine Goldfische angelegt.
(My father built a small pond in the garden for his goldfish.)
Der künstliche Teich im Stadtpark muss einmal im Jahr gereinigt werden.
(The artificial pond in the city park must be cleaned once a year.)
Früher nutzte die Mühle das Wasser aus dem angrenzenden Teich.
(Ideally, the mill used the water from the adjoining pond.)
Zuchtforellen wachsen oft in einem kontrollierten Teich auf.
(Farmed trout often grow up in a controlled pond.)
Weiher
C1A Weiher is a small, shallow standing body of water that can be natural or man-made but usually lacks a technical device to drain the water.
Wir treffen uns im Sommer oft am Weiher zum Baden.
(We often meet at the pond within the summer to go swimming.)
In der Mitte des Dorfes gibt es einen alten Weiher mit vielen Fröschen.
(In the middle of the village, there is an old pond with many frogs.)
Der stille Weiher im Wald ist ein Paradies für Libellen.
(The quiet pond in the forest is a paradise for dragonflies.)
Da der Weiher keinen Abfluss hat, war das Wasser im Sommer sehr warm.
(Since the pond has no drain, the water was very warm in the summer.)
Summary
Use Teich when describing a man-made body of water designed for a function, such as fish farming or garden decoration, which can arguably be drained. Use Weiher for a more natural-seeming, shallow body of water often found in nature or villages that usually maintains a permanent water level without active regulation.