To find the water level of the river at the end of summer, you need to add the two elevations below sea level together.
The initial water level is at \(112\) meters below sea level, and during the summer, it drops another \(213\) meters below sea level.
This can be calculated as follows:
\[ 112 + 213 = 325 \]
This means at the end of summer, the water level is \(325\) meters below sea level. Therefore, the final water level is:
\[ \text{Water Level} = 325 \text{ meters below sea level} \]