Some of the fellow riders told me that they didn't ride south side of the Arenal Lake circle because of inability to cross Cano Negro.
I did ride this road twice and it is my favourite area in CR. Please do not give up on trying!
First time I did it with organised group and support vehicle, west to east. We made it over the river with just the bikes but SAG van got stuck in the middle of the river. While waiting for the van, night rolled in. We had to continue with the moon light and fireflies showing us the way. It was unforgettable! Van waited for big truck to pull him out.
Second time, I did it by myself, fully loaded, east to west. It was end of January.
From the banks it looks scary, fast and big, but don't get discouraged. It's all in the head.
You have to unload the bike and make multiple trips over the river!
At the deepest it's around 60cm but it's fast with big rocks on the bottom. With hands full of stuff, You can easily lose your balance so take it easy and double check every step. Water is refreshing.
That section is only 10-15m wide, the rest is easy and manageable no problem.
The rest of the south lake route has 4 more river crossings but they are all easy and don't require bike unpacking.
Hope that you make it over there and see why I love it so much.
Happy Riding!