Which of the following instruments is used to measure the speed of a stream?

The instrument used to measure the speed of a stream is a simple float. This involves placing a floating object, such as a cork or a ping pong ball, in the stream and measuring how quickly it moves downstream. By timing how long it takes the float to travel a certain distance, you can calculate the speed of the stream. This method is useful for monitoring the flow of water in a stream or river, which can be important for predicting floods or understanding the health of aquatic ecosystems. The other options listed are not used for measuring the speed of a stream: - A Secchi disc is used to measure water transparency or clarity. - A quadrat frame is used to measure the distribution of plants or other organisms in a particular area. - A rain gauge is used to measure the amount of precipitation that falls in a particular area.