What is the depth of the water?
The water is shallow.
    src        edge_attr  dst
0     1               in   18
1     1        flying in   18
2     2      flying over    9
3     3      flying over    9
4     4               in   18
5    11               in   18
6    12      flying over    9
7    13      flying over    9
8    15               in   18
9    15   to the left of   19
10   16      flying over    9
11   17               in   18
12   19      flying over    9
13   19  to the right of   15
14   20      flying over    9