Step 1: Identify the lake:
Sudarshan Lake was an artificial reservoir situated near the Girnar hills at Junagadh in Gujarat, an important irrigation work of ancient India.
Step 2: State who built and repaired it:
It was originally constructed under Chandragupta Maurya by his provincial governor Pushyagupta Vaishya; Ashoka's governor Tushaspa later added irrigation channels/conduits from it; it was repaired again by the Western Kshatrapa ruler Rudradaman I after a breach, as recorded in his famous Junagadh rock inscription (c. 150 CE).
Step 3: State its significance:
The Junagadh inscription of Rudradaman I describing this repair is one of the earliest long Sanskrit prashasti (eulogy) inscriptions and a key source on ancient Indian irrigation and administration.
Final Answer:
\[ \boxed{\text{Sudarshan Lake: Mauryan-era reservoir at Girnar, Junagadh; repaired by Rudradaman I (Junagadh inscription)}} \]