What is the river surrounded by?
The river is surrounded by the grass.
    src        edge_attr  dst
0     0   to the left of    5
1     2      surrounding    9
2     3   to the left of   12
3     3   to the left of   14
4     5  to the right of    0
5     6  to the right of   11
6     9    surrounded by    2
7    11   to the left of    6
8    12  to the right of   14
9    12  to the right of    3
10   14   to the left of   12
11   14  to the right of    3