Your question is very interesting.  The attached film is related and presenting the issue clearly. 

I think you can improve your presentation by writing the question and the answers more clearly. 

 Here is my suggestion to rewrite the question:

Algae blooms in lakes and seas occur in specific environmental conditions.  The bloom is a seasonal but some years it does not appear at all. Under certain conditions a  massive blooms accurse. 

Please watch the attached film and figure out what are the environmental condition that increase Algae blooms

 And the right answer should be:

The bloom consists of a large number of cells in a very high concentration that forms colonies.

Strengthened when the following conditions are met: the water has a high concentration of nutrients  in the lake . In addition, the weather conditions are good for the algae - sun, heat and lack of winds are perfect for creating a rash.

It is the first time I read about Algae and Algae bloom, and I enjoyed reading your question and gained knowledge - high quality question.

I have few comments and suggestions, and for that I would divide your entire question into several items:

1.       The introduction (Lake stratification):

Good and short intro of the phenomena. As it is a new concept for me, I quickly understood it and I think it is well serves its purpose.

2.       Graph + text (on the temp. depth & nitrogen):

Great to have graphics in the question which can explain a lot w/ minimum text. The graph and text are good but I think it can be better: the text section beneath the graph can be reduced and you may add notes and arrows on top of the graph so the graph will be self-explanatory e.g. adding note to explain the black lines, another note for the orange and the blue sections. Thus the learner can find a much of the info he needs in one place (the graph).

In addition, you may add the global-warming concept in the text section as it is related to the rising of the temperature.

3.       Video (Algae bloom in Lake Erie near Toledo, Ohio) + View points on the map:

These 2 parts show excellent and various examples of the issue, the relevant parameters, the risks, affect on humans/animals (echo system) and ways of dealing w/ that. They show that the issue is a global risk (points in the map from US, china, Israel) – very important for the learner so he can be more connected to the issue.

I would have reduced the amount of text and the font size in the Western-Coast video (point in the map – San Francisco) – the video tells almost all the info you need on that example.

I would have added text to the china point in the map, short explanation about the example in china – not a must but nice to have (the video shows all you need to know).

Change text format in the Eilat point: the sentences are very long, going out of the normal frame – technical issue.

Too much text in the Yigal Alon Laboratory point, I have a suggestion for text improvement:

"The Kinneret Allon Limnological Laboratory (A.K.A KLL) is a relatively big laboratory w/ the following goals:

Most important goal is determine whether the quality of the water is good enough for national supply or not (by collecting weekly samples from different places in the lake, analyzing them, which will be transmitted into real-time data for laboratory database) – many chemical, physical and biological parameters in addition to major environmental factors are being measured.

Monitoring activities to provide data, information and advice to several related governmental agencies working in the area – growing importance to these activities.

Examing topics e.g. the structure and function of the lake ecosystem, responses of the lake ecosystem to water level fluctuations, the effect of human activities and agricultural/urban developments on the lake system, transport processes of nutrients and pollutants into the lake and their bio-geochemical cycles within the lake and many other topics.

These activities are being carried out by 30 scientists, research assistants, technicians and students carrying out research projects for advances degree."

4.       Question itself + answers:

Very relevant question to the subject as it is not only related directly to Algae bloom but also integrates all the aspects shown in the intro, grap, text, video and the points on the map. I think that for a learner to answer correctly, he/her should understand these aspects well before answering the question.

Summary:

I see a strong correlation between the question parts, each part is relevant to the subject (Algae Bloom), adds info and each part is complementary to the other parts, thus creating almost a full picture to the learner.

The contributions by each part to the entire question:

·         Scientific and technical background: contributed by the intro (Lake stratification), the graph and the text section.

·         Examples around the world, risks and impacts on echo-system: contributed by the video and the points in the map.