IELTS Writing- Task 1 ( please help me correct this note book, thank you )

The picture below shows information how regarding the (using the phrase regarding vs. how is more professional) Red River's (in English, you capitalize the full name of rivers) discharge rate had fluctuatedion (easier to change this into a noun clause) over the period of 12 months in 2013.

In the first month, it was observed that the discharge of the rRed rRiver stood at 1000 cu ft/sec and then remained flat (remained by itelf it not descriptive.  We use remained high, remained, low, or remained flat) for the next 2 months. In April, (In April is a prepositional phrase to start a sentence so you need a comma) the static trend was broken suddenly, when the discharged rate increased significantly to almost 18000 cu ft/sec. However, there was a decrease of 15000 cu ft/sec over the next two months in June. August came with had a very strong rise back to over 25000 cu ft/sec. This upward trend was broken sharply in the next month and when the rate fell to just to almost 8000 cu ft/sec. This was followed by a another fell steadily fall for the last 3 months and in December, the discharge rate had the same level as they it had  were in March (the phrase this is referring to is 'discharge rate', which is singular noun so you need "it had"rather than 'they were").

Overall, the discharge rate of the Red rRiver fluctuated strongly over 12 months, especially the period from March to October. September was observed as the highest number while January, February and March were fairly equal.

Hope this helps!