Shallows
noun
The high rapids are the shallows. How does that make sense?! I guess this means geographically high. So higher up the river, near the source, the water tends to be pretty shallow.
You'll see 高瀬 mostly in names, such as 高瀬川 (Takase River) or 高瀬ダム (Takase Dam).
The reading comes from 高い and the reading you learned for 瀬.
この川はこの辺りは高瀬になってるから、きっと足が底に着くと思うよ。
The river is pretty shallow around here, so I’m sure you’ll reach the bottom.