Narrows, in the context of a navigable waterway, refers to a constricted or tight section within bodies of water such as straits, rivers, and channels. This stretch is characterized by its lesser width compared to the surrounding body of water, resulting in a spatial constraint that can impact the flow of water and the passage of vessels. The feature may occur naturally due to geographical formations or places where water is channeled by landmasses on either side, or it may be a result of human-made infrastructures like bridges or dams. As a critical element in nautical navigation, 'narrows' generally demand heightened caution from mariners due to increased risks of collision, grounding, and stronger currents.

1. The Gibraltar Straits, a narrow waterway connecting the Atlantic Ocean to the Mediterranean Sea. 2. The Bosporus, a narrow strait in Turkey that forms part of the boundary between Europe and Asia. 3. The Panama Canal, a man-made waterway that narrows at the Culebra Cut. 4. The Cook Strait, the narrow waterway separating the North and South Islands of New Zealand. 5. The Malacca Strait, a narrow stretch of water between the Malay Peninsula and the Indonesian island of Sumatra.

One of the most famous "narrows" in the world is the Strait of Gibraltar, which is the narrowest point of the navigable waterway connecting the Mediterranean Sea to the Atlantic Ocean. It is only 14.3 kilometers (8.9 miles) wide at its narrowest point. Despite its narrow width, it is one of the most important navigable waterways due to its strategic location and is heavily trafficked by commercial and leisure vessels. Moreover, it's considered a key chokepoint in the global sea trade routes. Interestingly, it is also known for hosting a phenomenon called the "Mediterranean Step", where the water in the Strait of Gibraltar has two layers – a warmer, less salty layer on the top, and a colder, more saline layer on the bottom, due to the Mediterranean Sea’s higher salt content compared to the Atlantic Ocean.