Final answer:
The waterfall is 13.6 km south of the lake, and no additional calculations are necessary as the distance mentioned is the direct distance between the two points along the bearing provided.
Step-by-step explanation:
The question is asking about calculating the distance from one point to another using bearings in a navigational context, which falls under trigonometry in mathematics. As a bearing of 228 degrees likely indicates the direction relative to the north (clockwise), the actual distance given (13.6 km) is directly the distance between the lake and the waterfall. No trigonometric calculations are needed because the distance mentioned is already the distance between two points (the lake and the waterfall) along the bearing of 228 degrees. Hence, the waterfall is exactly 13.6 km south of the lake.