3. In the middle of summer, I spent a week on a Lake.It is located at an altitude of almost 2 km above sea level. I was fishing, roasting fish over a campfire, riding a boat and a zip line and enjoyed the fresh mountain air there.
4. From the beginning of the summer, I started practising a new sport for me - boxing. I was lucky enough to train with an international coach.
5. In my free time, I watched scientific films, read and just enjoyed chatting with family and friends. It was a wonderful time.

https://en.wikipedia.org/wiki/Standup_paddleboarding
И почему в 2 и 5 past indefinite, а в 3 - past continuous?
не думаю, что вы можете RIDE a boat. https://www.italki.com/en/post/alSmmb216Y9DvkGidaNrm1 . Насчет SUP тоже сомневаюсь.
a new sport - boxing
was lucky to be/get trained
что такое international coach ?
...

Elena, why are you asking an app full of Russians about English? Do yourself a favor and make an account on journaly.com and get help from natives. 

Спасибо!

If you join, please let me know — I’d be happy to correct your posts.

Барбекю и пикник одно и то же, наверное.

of summer - артикль?

holidays , s не нужно (?)

I spent a week on a Lake. At the lake

Барбекю и пикник одно и то же, наверное.

Нет. Барбекю может быть и (около) дома, а пикник может быть и без барбекю.

the fresh mountain air there. The не нужно.
На меня не ориентируйтесь, я сама учусь)

Grumbler, будем знать.

I had started (?)
... Lake.It is located (which located)

started practising a new sport for me
Я не уверена, но мне кажется practicing не нужно. For me , наверное, тоже лишнее.
I have started doing some new sport. (?)

Мне просто интересно поучаствовать)

@ULY Thank you for your advise. I have joined right now. Handle is Zuliasha

adviCe

Elena, I’ll look out for your posts 😉

I just read it. Excellent first post!