Probably the lake has an excess of phosphorus and nitrogen. There is no easy way to solve this. Maybe the introduction of native Floating-leaved macrophytes can reduce the nutrients levels in the water collum and provide shadow that limits the light penetration in the lake. Another act could be growing plants in the side of the lake to avoid the input of nutrients by the drainage basin.

agree with Marcos Sarmet Moreira Barros Salomão ... the lake water has high content of nutrients... first of all you have to find out the source of nutrient and if possible stop it. It may take time.

to get quick result you can manually collect them and use them as bio-fertilized. yo can also culture herbivore fish species. it will solve your problem and will not harm bids. again, the permanent solution is stopping nutrient flow from outside the lake

Liming in measured doses

So true Abhijit Mitra

Marcos Sarmet Moreira Barros Salomão Shahab Uddin

thank you for your answers

but the only source of nutrient is the birds fecal dropping, nothing else.

and we can not use fish or plants, because we have some fish-eater and plant-eater birds too!

Abhijit Mitra

Omar Ali Al-Khashman

thank you for your answers.

but what kind of lime we can use?

and is it friendly to birds which drink from that water?

Do you know if there is a healthy population of zooplankton in the lake? If not, you could try adding some from another pond/lake. Some zooplankton will feed on certain phytoplankton, which can help keep blooms in check.