how can I find the coordinates of the central axis of a river in an image (binary)?

I am trying to find a vector that contains the midpoint or talweg of an image of the Valdivia River (Chile) To do this I am using a code that I found on this page, I attached it. The problem is that with the example there is no problem, but when changing to my image I get an error. help!!

https://la.mathworks.com/matlabcentral/fileexchange/66779-algorithm-for-finding-the-center-of-a-river-of-an-image?s_tid=srchtitle

the "1.png" image can be downloaded from the link.

clc
clear all
a=imread('1.png');
imshow(a);
impixelinfo
b=im2bw(a);
figure,imshow(b)
imfinfo('1.png')
impixelinfo
E = edge(b);
figure;imshow(E)
c=imcomplement(E);
figure,imshow(c)
impixelinfo
[col row]=size(c);
k=1;
count=1;
for i=1:col
for j=1:row
    if c(i,j)==0
        [j i]
        if i==i
       z(k)=j
       k=k+1;
       g=i;
        end
        count=count+1;
    end
   
end
k=1;
     if (z(2)-z(1))>2
    av=(z(1)+z(2))/2;    
    hold on
    plot(av,g,'.')
     else
     av=(z(1)+z(3))/2;    
    hold on
    plot(av,g,'.k')         
     end
     
end

Answer 1

[Matt J]

load River

C=watershed(bwdist(A))==0;

[icoords,jcoords]=find(C);  %coordinates of center line

imshow(A+C)

[Adam Danz]

Great approach!

Where did A come from?

[Matt J]

It's just a cropping of the image in the original post.

[Hernán Madrid Oyarzún]

thanks, works perfectly and it´s very simple,

Now i´m trying to find the coordinates of the north or south banks to can find the width of every point of the line detected by this process. if you can help me I would appreciate it a lot.