I was initially shocked yesterday when I saw pictures and videos of the event at the Kara section of Ogun River in Lagos State. I read comments on Nairaland and listened to an interview of a Marine Scientist from the Oceanography Institute on Channels TV. The explanation provided by the Scientist was too general in my opinion. After thinking deeply about what could be going on, I came up with some scientifically-supported and logical assumptions based on general knowledge about ecology of rivers, and related natural systems (geologic, etc).

This is Unlikely (though there is no information or activity to support or disprove it
1. A Geologic Event: disappearance of the water into a sinkhole or a newly created "fault-line". Though there was news story few weeks ago about an earth tremor in Saki, Oke-Ogun area of Oyo State (http://www.vanguardngr.com/2016/06/earth-tremor-causes-panic-oyo-community/), an area that I believe is part of the catchment of the Ogun River. Unfortunately there is not information to support this assumption.

In my Opinion, This is More Likely
2A. An exponential increase in Water Hyacinth in that part of the river due to abundant nutrients introduced into the water from human activity around the immediate catchment (e.g. animal and human wastes from Kara Market, and nearby communities), plus supplied nutrients from areas upstream of the river especially from the recent rain.

2B. An increased growth of Water Hyacinth also led to an increase in the amount of dead plants that get deposited at the bottom of the Kara section of the River which are not quickly broken down as there is less supply of oxygen at the bottom.

2C. An unusually high deposition and trapping of sediments in the Kara section by dead plants at the bottom as well as other living plants body at the upper section, following the recent heavy rain. This mean that a lot of sediments came with the rain as usual but a lot of that sediments get trapped in that section of the river because of what is explained in 2A and 2B. Observe the land use activity just above the river (in the image below) where the land is almost bare. Huge amount of sediments could have come from areas like this.

2D. A pronounced tidal flow downstream (between 17 - 18th of June) from lower section of Ogun River into the Lagos Lagoon and further into the Ocean, which PULLED-OUT any available water in Kara section of the river with it.

2E. After the event above (in 2D) the water in Kara section of the river could not be replaced because water from upstream areas cannot flow into the Kara section of the river since that part is blocked or flow of water into it very low due to the situation explained in 2A and 2B.

2F. If the event in 2D truly occurred, one would expect an inward tidal flow of water to occur later to replace what was taken away but the water could have gone to other parts of the Ogun River catchment since the Kara section is blocked.

Note: these are mere factual assumptions. Data on recent tidal flow, water level around the catchments, and investigative activities is needed to support this. I am not sure Nigeria has a very responsive science community, if not, information should have been flying around to help people manage their curiosity and bewilderment on this event. Some say it's a miracle. It's probably not. Help yourself with the images below.

AJL2 has a Master degree in Environmental Science and a PhD in Biology; he has participated studies on the Lagos Lagoon. He live and work in North America.