here I sketched some ideas out. There are some main components to speak of.

Solar oven style reflectors using 6mil

Black steel thermocollector in the center of the oven

Seeback effect thermo electric generator with ultra low DV sensitivity to collect heat to voltage transfer

Petals balance the own on the water and keep it up right

Under the solar oven in the water is where the heat transfers to, a small water pump pushed water through a aluminum cooling block on the cold side of the TEG chip which in this small example is 40mm squared. Not just any TEG will Work as they unit needs to be optimized for electrical generation between 150c and 190c hot side temperature. The water in the river stays around 55 to 65 degrees on a hot day.

In additional to the thermal collection a helix style or similar hdydro powered generator can be mounted underneath. Here we have 480 miles of river averaging 3 ft per second movement on the surface and even more under the surface

I would love to mimic the natural shap of a water Lilly which in nature floats on the surface while collecting light for photosynthesis.

On each petal I am considering a small solar panel not for the actual generation of the power , but to support the cooling pump to prime and start each morning or after a hard rain where there is little heat to collect this the cooling pump would stop.